Top 10 Rules That Rarely Show Up in DnD 5E 

Video re-uploaded to fix some spell errors that were in the first version released earlier today.

My favorite niche rule is climbing on larger creatures. It rarely would have any sort of benefit, but I've always wanted an opportunity to utilize it.

For reference, the dexterity breaking initiative ties rule is actually in the rules for 3rd edition, which is why a lot of people just assume that's how it works in 5e.

I think my favorite overlooked rule is that darkvision doesn't see color. I've had great success as DM placing color based puzzles in lightless rooms, and the party struggled to figure them out, since they all had darkvision that they relied pretty heavily on. Made the players think, and they stopped thinking they could easy mode everything.

The most niche rule I know is that for effects whose area is a line, cone, or cube, it is up to the caster to choose whether the point of origin (generally, Self) is part of the area of effect. I have only come up with one application of this rule so far: If you have immunity to some chromatic dragon's breath weapon damage type and acquire the corresponding dragon mask, when you are hit with an effect dealing that damage type, you are instead healed (for half of the would-be damage). So if you manage to, say, gain immunity to fire damage and grab the red dragon mask, you could include yourself in your castings of Burning Hands, grabbing some free healing as you damage your foes.

The long rest rule may exist solely to hurt coffee-locks, Warlocks that never long rest, instead short resting 8 times and juicing the warlock spells into sorcerer spell points, to then convert into sorcerer spells. Sorcerer spells only reset on a long rest, so as long as you don't long rest, there's no cap to the number of spells you can have.

You don't just need suffocation rules for watery campaigns, gaseous monsters/traps and grappling can provoke it too, always interesting to see the players' realization. Didn't know about the alternate traveling activities though, I'll have to see about implementing them.

I think the alien technology rule is kind of weird unless you learn something for each int check you succeed. It's very gamey if you go from knowing nothing at 3 checks to knowing everything at 4.

Playing out travel is probably one of the must fun ways to add some more flavor and worldbuilding in your campaign. Both by adding natural obstacles and enemies. I once had a group that was tasked to investigate weird occult goings on in a town in a swamp. Now, none of them prepared for the journey, and they brought a cart and donkey. So when they arrived at the swamp, we had a very interesting situation, where they had to play out trying to get through the marshy terrain. It was really interesting for everyone involved, and in the end, they had to abandon their cart and donkey, as after some back and forth trying to get through the terrain, and the necessary rolls, they realised, that if they kept going at that pace, their provisions would run out days before reaching the town. And even dropping the cart, they only barely managed to make it there in time. It made for really cool RP without having to through monsters at them. Yet I think I never saw a party so relieved, when they finally made it, and got to rest in a tavern again.

0:35 I always have tied creatures roll some sort of sub initiative, so they both act on the same count, but the sub initiative determines the order on that count. Edit: 12:42 When you are always aware of everything and can't sleep anymore: The problem with being faster than light is that you can only live in darkness.

Interesting point to add to number one, when youre alseep you have the unconscious meaning " An unconscious creature is incapacitated (see the condition), can’t move or speak, and is unaware of its surroundings" focusing on the unaware of its surroundings ide rule that means the creature has disadvantage on perception whilst asleep ,which would in turn make the passive a -5 based on passive score rules

One rule I use for suffocating is that if they're dying and still suffocating, like if they're drowning, they suffer a failed death save at the start of their turns, as if they took damage. Even while dying you still need to breath. While optional, this can make underwater encounters, gas chambers, or monsters that eat players more dangerous.

5:31 the only time ive encountered casting long casting time spells in combat was when our party was in the deep ethereal looking for a god, and we had to defend the high level celric npc from waves of elementals while he tried to cast planar ally

Now, I'm imagining a couple of adventurer's, who are also lovers, whispering sweet nothings to each other while on watch, and the high perception ranger, just trying to get some sleep, hissing at them, "Would you two shut up!"

for the long rest and resting in armor bits: i usually rule that if a character is used to life as a soldier, you can sleep in heavy armor and can get a long rest as long as there are 2 short rests in that 24 hour period (usually a background bonus for my players that take a soldier background)

The ranger character is useful for not being lost. Especially in a favored terrain.

The rule that comes to my mind is the rule of Diagonal Movement. It is an optional rule that basically says that when moving diagonally, the first square costs 5 feet of movement, the second costs 10 feet. Using this rule, it basically costs the same amount of movement to get to a square diagonally as it would to get to the same square vertically and horizontally. I have not seen it being applied very often though as most people just seem to go with 5 feet of movement per square, regardless of where that square is in relation to you.

2:19 I actually had this rule come up recently in my game. I’m playing a monk and our ship was being attacked by giant sea turtles. Thinking I was being brave and heroic, I ran and jumped on top of the sea turtle, who promptly dove into the water with me clinging on in order to fight it (DM gave me an athletics check, which I passed). I used basically every spell and monk ability I had and ended up killing the creature under the water, but I was nearly unconscious if it wasn’t for my con modifier giving me 1 more turn to swim to the surface.

Mob combat from DMG. Rather than rolling individually for a large group of monsters, there's a table which shows how many creatures required to score a single hit. Subtract the creature's To Hit bonus from the target's AC, this gives you the minimum D20 roll. A roll of 1-5 requires 1 creature, 6-12 requires 2, 13-14 requires 3, 15-16 requires 4, 17-18 requires 5, 19 requires 10 and 20 requires 20. So if you have 20 goblins (+2 To Hit) against the Rogue with 16 AC, 1 in 3 goblins would hit. If all 20 target the Rogue, that's 6 hits. If they instead target the Paladin with Plate and Shield (AC20), all 20 gobbos must attack them to score a single hit. You can take the horde, subtract [x] number of units to inflict [y] number of hits, and roll individually for any unused units. And, of course, as their numbers dwindle, revert to individual dice rolls when it becomes impossible to hit using these rules. Although you forego any chance for a critical hit, this speeds up combat that would otherwise slow to a crawl. This typically never comes up as generally, DMs will try to keep encounters simple to ease the burden on themselves and maintain a good pace.

Using dex for initiative ties caused issues where the lower dex caster was unable to cast the beneficial spell that would have been a major benefit to the higher dex PC, specifically the bard wasn't able to cast Faerie Fire to give the rogue advantage. Using the proper rule of having players decide allowed the party to make better choices. I have used the breath holding rules a few times in my campaigns. Having that giant octopus drag the important NPC underwater meant that the party had to change tactics to keep them from drowning. Also tying Knots has come up a few times. I love all the expanded tool proficiency rules and DC checks in XGTE. I created basic feats using this section and give those feats to anyone with that tool proficiency. It has greatly increased my players use of their tools when problem solving. I try to include some of the DMG Chapter 9 rules in my campaigns as well. Last week I allowed the paladin to disarm a target of their weapon using the rule listed there and even had a great session testing out the cleave mechanic when the party was overrun with a huge pack of jackals at low levels. Watching the reaction of the player as their paladin sliced through 5 monsters with a single swing might have been one of my favorite early DM moments.

Also I'd love if you did more of these videos! Theres so many helpful rules that people just dont know/use and it's a shame.

As a DM who has had most of these situations cone up… I feel called out

The sleeping in armour rules are something ive looked up surprisingly often, mostly because i tend to play frontline characters. Though I have a tendency to just take off my armour anyways unless i am expecting troubles, simply because it is just too uncomfortable otherwise.

Neat analysis video! Thanks for uploading!

Interesting video. I knew some of these, but not all of them. Some sound excessive, but other can be pretty useful, depending on the style of play your group adopts. Cool! Thanks for sharing.

Awesome stuff. With the visibility range clarified, I see they're taking the Hobbits to Isengard! :)

I've been playing for a long time, so I actually know most of these, but there were a couple I didn't know. Great video

It's funny seeing the travel rules described as niche because in my circles they're one of the main examples used when talking about how the "exploration" pilar kind of sucks

regarding the drowning and suffocation rules, in the PHB under the examples for possible Con checks that the DM can call for it lists "holding your breath" as an example. This means that if you are holding your breath underwater the DM can ask you to make a Con check if you attempt to do other activities while holding your breath. I also treat holding breath as a concentrating mechanic. Meaning if you take damage while holding your breath you'll need to make a CON save DC 10 or half the total damage if higher than 10. This way suffocation is much more of a threat and possibility and the characters can even use it during combat to kill enemies.

That feel when I knew literally every one of these, and use them regularly in my games. Feels good, man.

This is soo useful, thank you!😁

These were very cool and nice to know Id love a follow up video

I once went without sleep for 7 days in a row. I was a basket case and baker acted myself on the eighth day (in Florida saying the words "baker act" to police, doctors or any medical personnel means you are immediately hospitalized for evaluation). I was certainly full of exhaustion levels. But I didn't die.

With the drowning; one round in DND is 6 seconds. So if you had a con of 14, you could be underwater for a total of 1(base)+2(mod)=3 minutes. There are 10 rounds in a minute. That's 30 rounds of underwater combat, bring a trident 😂

I used the sleep deprivation one when I was putting my group through a haunted castle.

Funny thing, in my group's first 5E game, we actually needed the drowning rules. PC with a lower level than a tied up NPC captive (enemy rogue) and the gang chasing him (also rogues). There was a lake and PC was an air genasi so to survive the constant attacks, keep the captive NPC held captive and potentially knock him out (or kill him if need be) so he stopped being a threat PC jumped into the lake and preceded to play tug of war underwater while getting very lucky with the disadvantage all of the NPCs had on attacking him

I think it’s important to use the travelling rules at least some of the time, especially if you have a ranger in the party. Their Favoured Terrain feature makes a difference since they can be alert for danger while also fulfilling one of the other tasks.

In regards to the drowning rules, the drowning time drastically decreases if they start casting spells with vocal components.

In the one campaign I played in that ran exclusively in 5e (the other 5e game wasn't in the 5e setting), Tomb of Annihilation, we dealt with Ties for Initiative (with players usually deciding based on DEX, since half the group was long time players), Going Without a Long Rest (this happened once because the Cleric decided to stay up in a repentance), Ritual Casting (always while the party was fairly stationary - like searching bodies after a fight - so movement never came up), Sleeping in Armor (nobody was wearing heavy armor because we'd be penalized wandering the jungle and we never had the opportunity). and engaging in Other Activities while Traveling (the vast majority of the campaign involved traveling through the wilderness without a known destination). I'm fairly certain all of these are in the PHB & DMG without need to reference later books. I think Xanathar's came out during our campaign.

Nice list.

Maybe I just played with crazy hard core players or have just put myself into too crazy enough situations, but I've encountered all of these rules, minus the sleeping in armor thing cause I played the fill roll and everyone else liked being tanky, more than once. To be fair, I think I aged my dm several years for some of my nonsense. Lolz.

I always deequip armour before resting and rarely wear armour in a town unless there's good reason to. Makes for more fun scenarios.

So you have game with 10 zillion spells & 5 gazzilion classes & subclasses to chose from but drowning is a niche rule?! Excellent stuff.

The rules for hypothermia, if you have cold resistance you are immune to it

Given that "higher dex is first" is a way that players can make up thier minds to break the tie, it's still a valid reading of the rules.

Hey D&DL, underwater rules; there's no long range, it's an automatic miss. Thanks D&DL you have a wonderful day!

Honestly the "going without a long rest" rule comes up often in our campaign as we often tend to either push ourselves to get somewhere faster or we can't sleep due to a traumatic event. However we have not implemented the proper rule of adding 5 to the DC on successes till you take a long rest. I as a Tasha's ranger abuse this mechanic as at level 10, you remove levels of exhaustion on both long AND short rests. So I can stay up all night doing research or brewing potions and then just sneak in a short rest in the morning or afternoon to negate the exhaustion penality. I call it, "the college experience."

We use suffocation (usually inside somebody rather than in water), going without long rest (we have really shifted balance based on one big encounter per day rather than adventurers day, but it still happen sometimes for some reasons), sleeping in armour (we actually couldn't sleep in heavy armour at all till certain moment, but then moved to classic), and also do something similar for initiative (players decide themselves, PC/NPC resolves with d12). Also, I guess it's some rule for swimming on a big depth even if you can breathe underwater, thought I don't remember it. I have newer understand, what is it even for.

I think the least used RAW is the length of activity that interrupts a long rest.

I think one of the least known rules in Dnd is falling on top of another creature. If you fall into another creature's space, it has to make a DC 15 Dex save or take half the damage and be immediately knocked prone. (Unless the creature is two sizes larger than you). Tiny creatures are not affected by these rules

10: wait its a niece Situvation. feels like that happen at least 1 every single round not session or battle but every single round at least two persons rolls the same. and only about half the time its between a player and a NPC (player always goes first in that case for us, exept if the player specific state that the NPC will go first). 9: the Suffocating rule can come up if you need to swim underwater it can also come up if you got a character that does not know how to swim or swim well (or stormy water where a failed roll will cause you to become take in water so to speak). that said I know of a few combat encounter where just punting a armored enemy into the water would auto kill it (or if the combat ended before hands the party getting the option to speak to the enemy while it ask for a hand to get out of the water, where by you ether help it on land or let it drown). 8: interesting on the exaustion as in our group it have always been whit a few exemptions you get the de-buff after 24 hour and the next one after another 24 hour. there was no roll for it you auto failed it. 7: did not know about that. that said we dont roll for everyday stuff exept if we want to make something extra. cheaf dont need to roll for everyday cooking if we got ample of supplies but if we are low or if he/she wants to make some moral boasting food then its roll where a crit fail usally means out of a ingridience or the food got slightly burnt. 6: Our group should really start using this rule more we dont. I do need to note some ritual spells does note that you can´t do them while moving (maybe need to draw a icon/circle on the ground surface, so on a cart or ships are still okey but not while walking on foot). 5: yee that rule we have them in mind sort of but there is usually a case of enemy ambush you in the night roll a dice to see if your sleeping whit armor or not (exept for if the player stated did or did not sleep whit armor on or off). we also does a roll on whose sift said ambush starts on exept for the times we specified who had what shift. 4: we never had this come up in our game except for the one time when we had magical weapon that when ever they struck something and did damage roll on a 1d10.000 table. where the only thing we got that is closest we ever had to interact whit this rule, target weapon is replaced whit a handgranade whit the pin removed and a 4d6(I think) blast damage 5 meter range next turn. mob just ran away and exploded thank good, that also means there is a universe where a soldier (we belive US) had his grenade replaced whit a sword. GM did inform there also was a working powered on laptop in the list. 3: the GM have always GM ruled it for us and I dont think it ever have came up for us. 2: another rule our group really should use more. that said there was a home brew rule I saw ones where all the skills listed gets buffed if your character have a relevant backstory. like if your a artist/cartographer you can sell the map for some cash in the next town, hunters(jobs, not ranger) can hunt animals for extra food). Navigate can auto succeed if they travel in familiar terrain (same country, or terrain type), Foredge was not really based on a skill roll but a forge table map/herbalist used the same map) 1: we had a homebrew solution and I remember it also had a case of over time because someone whispering one word would 100% never wake anyone up even a 20per person at 1 meter away. also our group liked to give slaps 1 point of stun damage (usually that would wake someone up but is not enough stun to stun them).

Other activities for traveling being number 2 makes everyone who has played or ran Out of the Abyss laugh. But, for everyone who has not played or ran OotA, makes sense. Also, for future videos: - Ten best / worst WotC campaigns - Ten most ridiculous character builds (either overpowered or simply most comedic is build [I have some doosies, even take to Twitter or something for community feedback]) - Ten best / worst class and race combinations

Toa gave us a chance to use the exploration rules

In my game, for ties i make tied players have their turn at the same time and for tied creatures same, if its an enemy and a player, players always go first

Well, guess we gotta boost the algorithm on this one

#4 I will spoil it a little bit, but not in a very helpful way. The old 1e module "S3: Expedition to the Barrier Peaks" has future tech. This module is actually the sequel to it more famous prequel that you can find even in 5e, "S2: White Plume Mountain". Originally both modules were set in the World of Greyhawk.

Having been DM for Out of the Abyss I have used every single one of these rules multiple times, except for the Alien Technology one, these rules come up a surprising amount in a lot of the campaigns I run and play in, I expect Alien Technology to come up soon though in my next few campaigns as we gear up for Spelljammer releasing.

Suffocation also comes into play when fighting an ettercap; some of them have web garrotes. I tend to extend this to a houserule: the existence of garrotes: really cheap, 2-handed finesse weapons that allow grappling with the escape DC related to the attack roll, only rogues get it added to their proficiency list, anyone else has to take the weapon training feat, because it's not martial or simple.

Lack of sleep can in fact be fatal in humans, too. I'm not sure how long the sleep deprivation has to be, but eventually the body and brain stop working properly.

We hand wave these travel rules if there is a ranger or druid with nature or survival proficiency.

Please note about the long rest causing exhaustion: to all the coffee lock out there, unless you are using the elven trance rule from Monster of the multiverse, which state that you do a long rest in 4 hours: Aspect of the moon allows you no NOT sleep during a long rest. you can do 8 hours of light activity (instead of just 2 hours) and you gain Exhaustion level on the lack of long rest (not the lack of sleep) So sure you can remain awake for 7 day in a row, but you still need long rest (resetting sorcery point and sorcerer spell slot) if you fail at doing that long rest (and resetting your sorcery point and sorcerer spell slot) you will gain exhaustion level So unless you wanted to also grab 11 level of ranger... and for the few elven coffee lock, I'm sorry to tell you that 4 short rest, to gain a few sorcerer point and convert them into even fewer sorcerer spell slot... you should have took more sorcerer level and instead of 3 extra lvl 3 spell slot, you could have gotten a level 4,5 and 6 spell slot...

Not going to brag, but I did know about all of these. Some of them I rarely enforce, due to saving time or working it into the narrative. However, I feel like these aren't more well known because they're just weird rules players don't pick up via osmosis, mostly because they don't own the books like the DMs do.

My first full campaign we unfortunately had to learn the suffocation rules because of an unfortunate encounter with a water elemental in a pool I say unfortunate but really, the party kept going into the pool to try and drag other people out/hit the elemental/just hanging out on the shore instead of just letting the only player with water breathing do it.

Damn, I didn't know you can designate more than the navigator/travel lead while traveling. And I AM doing a campaign where traveling exploration is kidna important (players move a party token on a hexa grid and explore the forest like that) Now of course it's not like they need to forage or anything so it's fine, but good idea to have other roles.

I abused the slanted floor/balancing rule once as a DM in a thieves' den in a 3.5 campaign. The floor was purposefully slanted and the room decorated to look normal like an optical illusion. In addition to balancing for movement range, any pc with a Dex mod lower than +2 (at that angle of slant) lost their Dex mod to their AC's.

Oh shit I didn't realize u made dnd videos too I thought you did wow and card games lol well new content I'll take it

Rules for building castles or other structures Also rules for gambling away all your money during downtime

the sleep deprivation rule never comes up because players usually try to long rest as soon as possible xD

Legendary resistance, never sleeps

The suffocating rule allows us to identify our CON score

Very logic

We roll off in a tie for initiative

I knew all but the visibility

I'm surprised suffocating was on here, you know how many times somebody gets stuffed into a bag of holding?

Basically, any rule that isn't part of combat, spellcasting, or skill checks.

Thank you! Concentration can be broken when the caster is hit. Do you know if this correct? Reality, I don't know people concentrate one thing and can do something else. Like patting your head and rubbing your stomach and count backwards. To have a intelligent check. Does this seem to fair to do? 🤔

I always just did a roll off if i rolled the same as somone else i never herd of the higher dex rule

I knew of all these rules except alien technology buy these rules are rather mundane and just slow the game down in my experience. If I told my players the consequences of falling asleep in armor they would just assume an ambush lol

*Laughs in 3.5*

One good rule is how far sound can travel

I’ve used most of these. For a few I’ve chosen to replace a few with homebrew or modified them a bit; after looking them up. Also remember to give -5 to passive perception for unconscious (asleep) individuals. I use this rule as stated I just feel the need to remind people here that the -5 defiantly applies in this case. I’ll add a couple more I like/use Climbing into a huge or larger creature, using alternate ability scores with skill and tool proficiencies, rules for darkvision (low light if total darkness and no colour) as well as rules for lightly and heavily obscured (as people seem to get these wrong a lot),etc. As for a few things I recommend replacing with better 3rd party or homebrew in 5e here’s a few; crafting mundane and magic items, foraging, use high DEX or roll off for initiative ties, falling damage and jumping (it’s an illogical garbled mess here’s my suggestion; unless an actively jumping creature lands more than 10 feet lower than the initial surface it jumped from it suffers no I’ll effect/damage. If it does land more than 10 feet lower than the level of the surface it jumped from it gets a Dexterity (acrobatics) check to avoid damage DC 13; 11-15 ft. DC 15; 16-20 ft. DC 17; 21-25 ft. DC 19; 26-30ft, etc. (choose up to DC30 for over 100 ft.) on a failure they land prone and take the fall damage and on a success they land on their feet (not prone if no feet), and take half damage. On a success of 5+ above the DC they take no damage instead. If a creature has a jump ability that allows them to jump more than ten feet add this to the allowed amount of distance before taking damage; ex a creature can leap 30 ft up from a standing start (such as from magic boots) this makes the distance before rolling the Acrobatics check become 40 feet lower than the surface they began jumping from. These rules apply ONLY to active jumping and allow PCs and monsters to be more consciously acrobatic and daring but increase the risk logically (I feel) also it removes the truly horrific RAW of creatures that can leap (grung, lions, etc) from taking fall damage when they land…. Which is so illogical and stupid…. Sigh. A creature actively leaping is totally different from an unexpected fall or being pushed off a cliff or falling into a pit trap! Also for creating new spells, rare materials, ‘masterwork’ or upgrades to non magic gear, etc. Please do homebrew but keep notes and write a copy for the DM binder and I highly recommend having cards with rules like these written out on hand. GM take the cards you are pretty certain may come up this serious out and ready behind your screen! Have the card with the ‘climbing on a huge or larger creature’ card ready if you are likely to make the PCs face one. Have obscurement rules on hand if fog will be present. Keep the card with darkvision on it handy all the time, etc! Or Modify or add common notes to your DM screen such as the darkvision and obscurement rules. Have cards for weather and other environmental hazards and common traps as well! Really very handy, can;t reccomend it enough! If you are sick of hand writing so many cards when you have enough work as DM ask some of your players to write out some that are not secret from them. For example; darkvision, obscurement, rain, heavy winds. Exile you write out the ‘secret’ ones like for traps and special hazards! Good luck everyone hope this helps.

one rule no one ever seems to understand is that passive perception doesn't actually spot traps. Throughout the entirety of the PHB and DMG there is no mention of it doing so in any block of rules passive perception is supposed to be a static value to roll stealth against even if you allow passive perception to spot traps, you still have to be looking in the general direction of the trap and be capable of seeing it (actually look at the ground to spot the tripwire, still miss the pressure plate under the carpet

As a DM the evil in me thought of a way to fuck with the player with a PP of over 20. You fuck with my campaign I fuck with your sleep. Would never do it but I like to think about it.

Can't get lost if you have a ranger in the group

What happens if you're a heavy sleeper?

Where are these travel rules from? A citation would be most welcome.

In the campaign my DM is running, rogue arcane spellcasters are put inside suits of plate mail, with straps secured by locks, as a means of preventing escape.

Wait wtf hiru has a dnd channel?

I've used suffocation as a player against an enemy. We were up against some roided-up berserker dude, and I used Mold Earth on the dirt under his feet to have him fall into the 5-foot hole (he failed the dex save to jump out of the way), dropping the dirt back on top of him, then piling more dirt on top of that. He couldn't dig himself out and died shortly later.

I new of the Armor ruling and as got a laugh out of it not being penalty enough as its very campaign specific as if your in a game where short rest are common then it might hamper but otherwise they'll wait 4 days for the hit dies they used to be restored as thats as often as they use them

I usually use a more punishing version of the first rule, where I give 1 point of exhaustion with no save to a character for each 24 hours they go without sleeping

I've literally used all but one of this rules. How the hell this are rules that "rarely show up"?

I've added the option for strong characters and monsters to use an action to squeeze out the air from the lungs once they have grappled the enemy (requiring a strength check against the con score as DC). Makes suffocation much more dangerous. Also, spellcasters, who use spells with verbal components underwater will also immediatly start suffocating after they cast the spell.

Actually, the drowning rules that say "minutes equal 1 + con mod (min 30 secs)" the 30 seconds refer to your con mod. Like if you have 0 or negative con mod, you get 30 seconds, but you still have the initial minute. So it'll take at least 90 seconds to drown someone.

Knew about suffercating, no long rest, armor in long rest and alien tech [specifically becase I'm running that ice based module]. Suffocating is stupid, it should be 5 rounds plus 1 round per con score [not mod]. With con saves to hold breath when taking damage or major exertion or lose half your remaining rounds. Then con mod of no air before unconscious. Also if forcefully dragged under, con save to result x5 = percent of maximum rounds of breath. [IE con score of 13, con save of 16, 16x5=80% of 18 rounds = 14 [rounded nearest].

Wait... 6:06 'losing concentration doesn't expend a spell slot' ? Where is this in the rules? Is it specifically only for during casting? Meaning, if I am ritual casting and get hit? So, in the situation where I wasn't going to use a spell slot then I'm not forced to lose one if hit? 6:18 - Oh, there it is. So, longer casting times than an action. So, casting identify with a spell slot only costs the slot if you finish casting it. Ah, I see... longer casting times just use the action each turn... I need a book and page number to show to my GMs. They never let us cast while moving... so we are forced to stay put to do any ritual casting.

I used drowning rules once in a session in this situation: the party was on a ship traveling to an island where they had been given a quest, while traveling they were attacked by a ghost ship and boarded, one player used shockwave and just another player was in range, the player failed the saving throw and fell into the water due to the shock wave. he was wearing half armor and for realism he sank from the weight of the armor to the bottom, since it would take a minute to take it off, we wrote that down and continued the fight, when the fight was over I looked at his constitution modifier (+1) and told him I said he had a minute left to swim to the surface. In the end I succeeded, but it was useful to take into account the rules, although it is true that it was a rather unusual situation :D

For 10, you as a DM want the players to go before your creature since you don't want to TPK them with something. For 9. It comes up very often if you use polymorph and want to instakill something using it. A polymorphed creature that is suffocating will remain suffocating when it turns back meaning its a way to kill any creature that needs to breath air

I wish these rules were more well know. I try to bring up the Initiative one whenever it comes up but DM almost always use Dex or a reroll.

Regarding sleeping in armor, our table has been misunderstanding it, based on LARPing experience and the levels of pain from sleeping in armor. Heck, even just sleeping without loosening your belt and shoes can mess with you. Our characters in medium or heavy armor don't sleep in their armor, which has had some deleterious results for night attacks. Even now knowing the rule, I don't see us changing our usual method on this.