25 Sonic Mania Easter Eggs You Might Have Missed 

At the beginning of chemical plant when a drop falls on his head. That is a reference to sonic spinball when sonic hops out of the water and shakes off.

Oh there's a lot missed out. Let's start with boss fights. Spoilers, obviously. 1. Green Hill 1's miniboss is a mixture of the original GHZ boss and Launch Base miniboss when played as Knuckles. 2. Green Hill 2 Death Egg Robot arm extension was adapted from Sonic Generations. 3. Chemical Plant 1 has some elements from Ice Cap miniboss. 4. Chemical Plant 2 is of course Dr Robotnik's Mean Bean Machine. The music is the 2 player vs mode in that game, which is also a remix of Satan's theme in Puyo Puyo. 5. Studiopolis 2's boss features the chicken badnik from S&K's Mushroom Hill Zone, that blows wind. 6. Flying Battery 1 miniboss is a mixture of Wing Fortress boss and the original Flying Battery 2 sub-boss. Also, just before the fight, you can see the blueprints for the spider boss fight in Act 2. 7. Press Garden 1 miniboss is a microphone, sticking to the media theme. 8. Press Garden 2 Heavy Ninja features sound effects from Shinobi. 9. Stardust Speedway 2's boss: The mini Silver Sonic is from Sonic 2 8-bit, and his spindash sound effects come from the 8-bit games. 10. Also, in that same section, Metal Sonic sitting in that position is taken directly from Knuckles Chaotix. 11. In the second part of the Stardust Speedway fight, we see the Eggman head building, seen only during the D.A. Garden and the end credits animation for Sonic CD. 12. Hydrocity 1: Eggman collapsing the building is taken from Marble Garden. 13. Also, the miniboss has Sonic and Eggman's roles reverse from the original Hydrocity 2 boss. 14. Hydrocity 2 boss features the original's miniboss from Sonic 3. 15. Mirage Saloon 2's boss is Heavy Magician with Team Hooligan. When he is in the box and it starts to warp, the sound effect is from Knuckles Chaotix after selecting a partner in that game. Also, when it transforms into one of the Hooligans, it's the sound of Sonic losing rings from the 8 bit games. 16. Oil Ocean 1's boss looks familiar, but can't quite put a finger to it. 17. Oil Ocean 2's boss has a mixture of the original Oil Ocean boss, with the giant octopus replacing the submarine and with guns from the original Lava Reef miniboss. 18. Lava Reef's 2 Sonic's boss is similar to Captain Whisker and Johnny from Sonic Rush Adventure on DS. 19. Lava Reef 2's Knuckles Boss features hilarious animated thought bubbles of Knuckles and his last encounter with Eggman in Sonic 3 & Knuckles. 20. Metallic Madness 1's miniboss is Sonic 1's Final Zone boss. 21. Metallic Madness 2's boss dispenses mini robot Amy. A possible reference to Sonic R. 22. Titanic Monarch 1's miniboss is S3&K's Death Egg miniboss with a twist. 23. The Egg Reverie boss: Eggman's machine is similar to what he had from Sonic 3D Blast's Spring Stadium and Panic Puppet boss. 24. Also, the Egg Reverie theme possibly contains tunes from Sonic Forces' theme, Fist Bump. 25. And lastly, Sonic Mania's miniboss theme's title is Danger on the Dance Floor. A nice nod to Michael Jackson's Blood on the Dance Floor. Sonic Fans should know Michael Jackson was somewhat involved in composing the music for Sonic 3. That's 25 for boss fights alone. I'm sure there's more to pick out. There's so many! Edit: Additional stuff thanks to comments below. 26. Mirage Saloon 1's Knuckles miniboss is the giant Catakiller Totem, similar to Sonic Chaos' Gigapolis Zone Boss. 27. Metallic Madness 2's Egg Dispenser boss dispenses three different kind of "Eggs". The boss from Sonic 1's Marble Zone, Sonic 2's Emerald Hill and Mini Robo Hugging Amy is a mixture of Sonic CD and Sonic R. In Sonic CD's Palmtree Panic, Collision Chaos and Stardust Speedway, she can be seen running after Sonic and hugging him. And she is modeled to look like the Tails Doll from Sonic R.

I feel like 12, 20, and 24 dont count as "easter eggs" flying battery taking 3 bombs instead of 6 is a design change, not a reference or anything, as its the same stage If you count oil ocean catching fire, shouldn't you also count the bridges in green hill zone burning too? and amy seems too well known to be an easter egg in this sense, maybe if you linked her clinging to you to how she does that in sonic cd then yeah, but just saying she's there doesnt feel like an easter egg

Here's some additional references: 1. The Green Tubes in the background, while fighting Metal Sonic and his remote controlled Silver Sonics are a reference to Sonic Adventure, where some green tubes with Metal Sonics in them appeared in Final Egg. 2. The actual device used to control the Silver Sonics is from Knuckles' Chaotix. 3. The bubble mechanic in Hydrocity is a reference to Sonic 2 and Sonic Triple Trouble on the Master System / Game Gear. 4. One of the enemies in Press Garden: the Bombbearer returns from Techno Tower in Knuckles' Chaotix. 5. The two bosses summoned by the Metallic Madness boss (in addition to the Amy Dolls) are smaller versions of the Marble Zone and Emerald Hill Zone bosses. 6. A Burrobot from Labyrinth Zone appears in the rubbish piles of Flying Battery Zone. Strangely this badnik doesn't return, despite being in the pile, unlike the other badniks in the pile. In addition to this, a turquoise badnik can also be seen, with a yellow part attached to the top of it's head (it seems to be a recoloured Roller but I could be wrong). 7. Most of the zones from Sonic 1, 2, 3&K and CD are referenced in the level design. Not all of them are though, if you don't count mechanics that were in the original levels to begin with (Tidal Tempest, as some of the original mechanics of Hydrocity were borrowed from there)

Press Garden Act 2 boss uses sound effects from Revenge of Shinobi on the Megadrive, quite fitting as the boss is a Ninja. The bubble mechanic in Hydrocity was also used in the Aqua Lake Zones in Sonic 2 on the Master System. Studiopolis Act 2: The chicken badnik (Cluckoid from Mushroom Valley/Sonic 3) displays a sun logo when its hot. This specific logo can be seen in the "handling this cartridge" section of the Master System game manual, more specifically "Do not expose to direct sunlight" This one is VERY obscure so not many people know about it.

6:39 Hyperdimension Neptunia & Knuckles. Bet ya some staff on the Eurogamer team is feeling cheeky right now.

Me before the video, "The majority of these are going to be in Studioplis Zone." Me after the video, "Look at how smart I was to make the obvious prediction."

Hyperdimension Neptunia & Knuckles, I love that reference as a Neptunia player

Studiopolis Act 2 uses a funnel mechanic that allows you to earn points depending on how long you spin in it. This is actually from Casino Paradise Zone in Sonic Advance, including the sound effects

18 Do you really think that we didn't know that was a caterkiller

Sonic getting hit with the shrink ray is an homage to Rad Mobile? Don't you think mini-sonic looks way more like the little icon you get after winning a Continue after a special stage?

In Stardust Speedway Act 2, taking one of the mini rockets leads you to a diamond of rings, a reference to Diamond in the sky from Sonic R

The metal sonic boss fight when he docks into the machine is a reference to his fight in knuckle's chaotix

26: in the beginning of the game, Sonic and Tails fly to Angel Island in a similar way to the beginning cutscene of Sonic 3. 27: When you play as Tails, the beginning cutscene shows Sonic driving the plane instead, and the goggles Sonic is wearing aren't just a random design, they're a reference to a beta element of Sonic 1 where Sonic could grab a pair of similar looking goggles to breathe underwater. 28: If you go into Debug mode in Green Hill, one of the placeable objects is a ball, referencing not just the first boss of Sonic 1, but also referencing Another scrapped item where the ball was going to be a gimmick for GHZ. 29: The original Splats is in the placeable items list for Debug mode in GHZ. 30: The mountain background in GHZ is a reference to a scrapped background for that same zone shown in a beta picture. 31: Mirage Saloon is a reference to 2 scrapped desert zones, Dust Hill from Sonic 2 & Desert Dazzle for the remaster of Sonic CD.

17b - If you play as Tails, the goggles Sonic wears are based on an unused item from the first Sonic game 18b - Knuckles version of this boss is based on the boss of Gigalopolis Zone from Sonic Chaos on Game Gear 24b - The Amy bots share some design elements with Sonic R's creepy Tails Doll character Also; - Sonic's animation when you first arrive in Chemical Plant appears to be based on the beginning of Sonic Spinball's Toxic Caves, where he jumps out of the water and shakes himself dry. - There's a sign in Studiopolis that lights up with the words 'GOOD', 'GREAT', 'AWESOME', 'OUTSTANGNING', and 'AMAZING', referencing the announcer from some modern Sonic games.

A Few of these aren't easter eggs... 12. Isn't really an easter egg, it's like saying ''Oh bet you didn't know the water in chemical plant is actually from sonic 2!'' 14. Not an easter egg either, it's, once again, a little throwback and a reason they go into the good future. 18. Pretty sure everyone knows that... 20. That's a gameplay mechanic... 23. That is actually just a reworked sprite from Sonic CD. Although, the original could have been based on that, I don't really know. 24. Not really an easter egg either, unless your friend is purposely blocking the TV or something. I don't really think any of those belonged in the video, but whatever.

Sound nerds will recognize the Sonic Spinball sound effects repurposed for the broadcast transitions in Studiopolis, the Infinite sound effect when the Pink Ruby distorts space time, and a very peculiar use of a Sonic SatAM sound effect in Titanic Monarch. But there are some visual gags and mythology nods you also missed. When Sonic transitions to Chemical Plant Zone he will get hit with some Mega Muck (Though in manuals it's called Mega Mack) which gives us a cute little excuse to shake himself clean. This is a cute little animation nod to Sonic Spinball's Toxic Caves. Also of note is the red and green plant robot in Stardust Speedway being a huge nod to an early Archie Sonic comic character named Krudzu who was a robot made to replace organic matter and snuff out Sonic and the gang. Also of note is that Bark, Bean, and Fang are a team in the comics known as Team Hooligan which makes their cameos as one solid boss battle a cute little nod and (maybe) a hint about the current direction of the series leaning towards incorporating the comics more. Also of note is that the machine that Metal Sonic is saddled in to make Silver Sonics is based on the same machine that Metal was birthed in in Sonic the OVA, making yet another alternate media appearance a huge thing in this game. It's cute how this game celebrates Sonic as an icon in not only games but in all media as well. It sounds like how they should have been doing this from the beginning if I'm honest. Hahahahaha One more for the comic nerds. Remember Sonic the Hedgehog no. 200 from Archie? The Spider Robot from that issue is a boss in Flying Battery Act 2.

No mention of the Shinobi boss surprises me. Bring on a Mania 2 I say. Plenty more thing from that generation they can reference and use.

The tiny Sonic in Metallic Madness is more just bringing back that mechanic from the original Metallic Madness in Sonic CD than a reference to something else :P Also the Mirage Saloon Act 1 boss could also be seen as a Space Harrier reference due to the way it's a segmented thing that heavily uses sprite scaling on all its segments to suggest it moving towards and away from the screen.

You can also see "wanted" posters for Bean, Bark, and fang in Mirage Saloon. Also in Mirage saloon there are rolling enemies taken straight from Spring Yard Zone in Sonic 1. Also Sonic's pose when he goes through the portal in the "true ending" seems to line up with the pose of classic sonic when he appears in the trailer (from the portal) in Sonic Forces o.O

Sonic's goggles when he flies the Tornado are a reference to an unused item from sonic 1 which would prevent you from drowning.

That's quite impressive. Well done, Ian.. & Knuckles.

5:57 I think that's actually a reference to the Extra Continue you get after a Special Stage in Sonic 2 / Sonic 3 & Knuckles, where at the Score Screen you see a miniature of the player character after finishing.

Number 11 is hilarious. & Knuckles

Sonic Mania was the most beautiful love note Sega could've ever given the fans. It's brilliant how every corner of every level has something to appreciate, be it endless retro Sonic references, rings placed to hint us towards secrets, or just innovative new gameplay that makes Sonic Mania insanely fun. I hope we get a Sonic Mania 2 in the future!

*smiles at a box with words* :sonic niiiiceeee

That mini Sonic is so cute! :3 And it's nice to see that SEGA actually remembers Streets of Rage.

A lot of people point out number 23 as being wrong. To be honest I think everyone is right about the tiny Sonic Sprite. There have been many versions of shrunk sized Sonic, all of which resemble the sprite used in Mania. The first time I seen it, I related it to the Original Sonic games, at the end of a stage if you got a certain number of points, you would get an continue, which was signified by a tune sounding like a piano or xylophone and represented with a small sprite of Sonic. A continue is slightly different from a 1up, continues were limited. They could only be used when the player got a game over screen. They would always spawn you back to the start of a zone, where as a 1up could let you start at any activated checkpoint in a zone. I think also after using a continue, your points would reset to zero again. All other game progression remained such as chaos emeralds. In Sonic 2 if playing as Tails, you got a continue he would have his own Tiny Tails sprite, which also looks like the shrunk sprite of Tails in Mania. But since these Sprites appeared in other games for different reasons, they could all be associated with the Mania Sprites. So unless the developers of Mania specifically state, if they based the Sprite on something in particular, there is no right or wrong answer for now.

23 is wrong. Tiny Sonic is a homage to his Continue sprite in the original Sonic games.

The Giant Caterkiller is also a reference to Sonic Chaos. Gigalopolis Zones boss was a Giant Caterkiller that shot its segments at you. Knuckles fights this same version of the boss in his version of Mirage Saloon Act 1

If you play as Tails, Sonic pilots the Tornado wearing the unused goggles from Sonic 1 (Which let him breathe under water). The Motobug the Lava Reef Act 2 boss rides is named Jimmy, after Polygon Jim, a well respected Sonic fan hacker, who made a fan hack where you play as a motobug, who unfortunately passed away. The wanted posters in Mirage Saloon are both a reference to "Team Hooligan" which Fang, Bark and Bean are all on, and to Sonic Generations, which had similar posters in City Escape Zone. The Press Garden Act 2 boss is a reference to Shinobi, using many sound effects from it. Knuckles' Lava Reef Act 2 boss if a reference to his final boss from Sonic 3 & Knuckles. I'll add more when I think of some.

Here's one you forgot, if you get the Knuckles and Knuckles ending, the song that plays the ending is a remix of the Knuckles Choatix title screen music.

When playing as Tails, seeing Sonic in the Tornado, Sonic wears the goggles which was scrapped from Sonic 1 to help Sonic breathe probably in Labyrinth Zone.

The Lava Reef act 2 boss is different for Knuckles. It also makes a direct reference to Robotnik stealing the Master Emerald in Sonic & Knuckles

18. has a bit of missing info: The Boss itself is a reference to the Gigapolis Zone Boss from Sonic Chaos. It's reference is more direct when you fight a similar entity with Knuckles.

I love the animation for sonic mania, it brings back so many memories and it reminds me of the old animated sonic movie I always watched

In green hill zone act 2, you can find the original start point of greenhill zone act 2 from sonic 1, if you do, you are rewarded with an extra life sitting where sonic would normally start. and an invincibility box in its usually spot in the trees. Was my favorite easter egg so far. just simply because you WILL miss it in normal gameplay because it requires you to backtrack and explore.

If you play through Lava Reef Zone act 2 as Knuckles, you'll meet up with a hard boil heavy and Knuckles think about what happen last time he went to grab the Master Emerald. A reference to Sonic 3& Knuckles.

I enjoy reading the comment section.

6:39 I LOVE NEPTUNIA

I'm pretty sure that the goggles that Sonic wears when flying the plane in Mirage Saloon Act 1 when you're playing as Tails use the unused goggle sprite that was going to be used in Sonic 1 whenever you went underwater.

When playing as tails, Sonic will fly the tornado, and will wear goggles as a reference to a canned sprite from Sonic 1 of him wearing the same goggles, presumably for underwater segments

What about how the sound effect when the Phantom Ruby activates is very similar to the sound effect when Infinite (from Sonic Forces) is revealed and activates his powers? Or what about the fact that Heavy Rider's motobug is named Jimmy, a homage to Polygon Jim, who created a rom hack for Sonic the Hedgehog where you play as a motobug rather than Sonic?

Well actually the mini sonic was based on the almost identical sprite of mini sonic in sonic cd

Wow, I didn't really think about adding to the experience. I just played through it, shrugged, and banished the game to the back of my Steam box. Now I feel really motivated to play, experiment, and take a full look at everything. ☺️

#11 is amazing! That's so clever and funny

You missed one big Easter egg, in Studiopolis Act 1 when you go inside the vans to teleport, you can hears the sound effect form Sonic Spinball when you are teleported to the other side of the area when you enter a hole.

In studiopolis, there is a reference to sonic colours, where one of the screens says "good, great, awesome, outstanding, amazing", this happens in colours when you do tricks

You forgot the part where knuckles rememred him getting shocked by eggman

0:09 Birthdayboi.exe has stopped working

The endboss of Press Garden Act 2 is a reference to Shinobi. They even use samples such as the Shurikan Deflect and Explosion sfx for that fight.

There is another grid of flipping letters un Studiopolis that say "WELCOME TO THE NEXT LEVEL", which if I remember correctly is an old punchline from a Sonic game commercial, and is written on the collector's edition box.

I seriously wasn't expecting no.25, it's funny

The toys shown for the Amy rose bit is Robotnik in his past machines such as the first boss in sonic 2 on sega genesis

Fantastic easter eggs list, loving it! Hope to play this one day.

The special stages are a combonation of many elements from games Sonic R (gameplay), Sonic 2 (chasing a Chaos Emerald), Sonic 3 (collecting blue spheres), Sonic CD (chasing a UFO), Knuckles Chaotix (using rings to increase time)

Ok, 11 was hilarious.

In Heavy Rider's boss fight, she rides a motobog named "Jimmy", which is a tribute to Polygon Jim, the creator of "Motobug in Sonic the Hedgehog". Polygon Jim died in a car crash in 2013, however. The eyes that Jimmy sports is likely a reference to Super Sonic from the Fleetway comics, as they both are faster than usual, and they tend to "rampage".

4:46 I SAW IT IT WAS BIG IT WAS ALL WIGLY AND IT ATE EVERYTHING, IT'S AN ALASKIN BULL WORM!

In Studiopolis there's a reference to Sonic Colors Announcer , were the dot-light sign on the bottom will say Good, Great, Awesome, Outstanding, Amazing.

Number 19: the sound effect when the box thing drops is the same sound effect as when sonic loses rings in the GG/SMS version of sonic 2

"These are the easter eggs we seen on our first PlayTrought" You Noticed that reference to a Obscure sonic PopCorn Machine on a Random part of a Zone? Me too!

The huge caterpillar boss of Mirage Saloon Zone Act 1 (Sonic and Tails) may actually be homage to another wonderful and interesting Sonic hacker by the name of Markeyjester, who is actually one of my favorites. In Markeyjester's "Jester's Challenge," you have to find your way through a huge maze. If you can find yourself through it, the final boss is a huge Caterpillar enemy from Sonic 1. Take a look at it, it's pretty neat.

At my community college theres a lounge where people play games. I once watched someone play a 5 hour binge of Dr. Robotniks Mean Bean Machine. There was at least 30 people there and everybody cheered when they beat the game.

25 Sonic Mania Easter Eggs You Might Have Missed "cuz im too fest" - sanic

Mirage Saloon Act 1 during the Tornado chase if you listen carefully you can hear a small clip of the Sky Chase music mixed in. Mirage Saloon Act 1 again, the boss for Knuckles path is the same as the Gigalopolis boss from Sonic Chaos on the Master System/Game Gear.

The buzzing sound from the livestream has me dying

At the end of one of the acts you run into robotnik operating a terminal. On its screen are the plans for capturing little planet as in sonic cd

The stairs around the end of Lava Reef Act 2 are a reference to S3&K/S&K, when Knuckles knocks a boulder down the stairs towards Sonic in the original as a "cutscene" to start Sonic's boss fight.

3:46 "Classic Sonic" and "Sonic" Excuse me, what?

There's also a neon sign in Metropolis Zone which says "To Be This Good Takes SEGA, To Be This Good Takes AGES."

Tails with pilot googles and knuckles with a cowboy hat is the best thing ever

The sound effect when you hit the ninja robot boss while he's mid jump is taken from revenge of shinobi when your suriken are blocked by an enemy

Also, Knuckles's midboss fight with the Caterkiller is a homage to the boss fight in Sonic Chaos's Gigapolis Zone.

Also the green tubes with metal sonics in them during metal sonics fight is a reference to sonic adventure where you could find the same tubes in eggmans mystic ruins base

holy shit, i didn't think 11 was that fucking genius

My mom found Sega Does last night. I screamed.

Might have already been mentioned, but the Act 1 boss in Mirage Saloon, while similar to the Catakiller, is also very similar to the boss in Gigapolis Zone from Sonic Chaos on the Game Gear, just a recolor, especially when you play as Knuckles, the boss from Gigapolis and that boss are almost exactly the same. Also the bubbles you ride in in Hydrocity are from the Sonic Games on Game Gear too, at least Sonic 2 and Sonic Triple Trouble. I was excited when Silver Sonic showed up. I had a Game Gear before a Genesis so all the nods (even Fang or as I knew him in Triple Trouble, Nack) were really nice touches.

Lots of gimmicks in Stardust Speedway Act 1 come from Marble Garden (Sonic 3). Also, Knuckles has an exclusive boss fight at the end of Lava Reef, reminding him how he was previously defeated by Robotnik in S&K.

No-one ever seems to notice that the Ninja robot boss has sound effects from Revenge of Shinobi. All his attacks and the noise he makes when hit are from that game.

I think you may have forgotten a secret 26th Egg that was added to Plus and can only be unlocked by the most godly of players. If you go to the Save Select screen, go to Game Options and set both Debug Mode and & Knuckles mode to On, then go back to the Save Select and enter the Konami code in very quick succession, then boot up Knuckles Chaotix on your 32X and enter the Colour Test, set the first four numbers to 4, 2, and 0 respectively, then locate Sonic Mania Plus's ROM file and enter the code 'game_sanity = GOTTA_BETSUNI_FAST_' in the ROM header, then immediately set knux_status to '69_BETSUNI_69' and convert that to the ROM header, while spamming the trick button over and over at least fifty times, you can unlock Maki Nishikino over Knuckles. I shit you not this actually works.

2:50 Only Sega would pay homage to something like that, and I love them for it.

Another addition to 19 - Fang, Bean and Bark were also heavily featured in the now-cancelled Archie Sonic comic under the team name "Team Hooligan"

#24 the little cars that Eggman shot out were from Sonic 1's Green Hill Zone Act 2 Boss.

"Genesis does what Nintendon't" MOST TRUE SENTENCE EVER SAID!

When playing as Tails in Mirage Saloon Act 1, Sonic is shown wearing some yellow goggles, as a reference to some unused underwater Sonic sprites in Sonic 1.

The giant catakiller boss (and more so for Knuckles) ismore influenced by the boss from Gigapolis Zone in Sonic Chaos (GG), with a regular catakiller skin applied. Also, Fang the Sniper appeared in Sonic Triple Trouble (GG), prior to Sonic Fighters, and Bean the Dynamite is from Dynamite Dux (Arcade and SMS)

The fastest running speed is a reference to some of the beta versions of Sonic 2. It was just tweaked and edited to match the style of Sonic in Mania.

18 is actually a combination of Caterkiller AND the 'Dangerous Ball Tower' boss from Sonic Chaos, and they even give it the square pupils it has on the US box art for that game.

There's a section in Studiopolis where a screen flashes the words "good, great, awesome, outstanding, amazing" in succession. A reference to Sonic Colors.

There's a good great awesome outstanding amazing sign in Studiopolis that you can find with some skilful flight with Tails. It is a reference to Sonic Colours.

In studiopolis act 1, there's a sign that flashes the words, "good, great, awesome, outstanding, amazing." This is a reference to Sonic Colo(u)rs and the sequence of words that appear when you go off a trick ramp.

Sadly, I just today learned of the "And Knuckles" meme. Chat commenting in a live stream. "Shadow and Knuckles" "Press X to Jason/Shaun & Knuckles" "Press X to have sex with Big the Cat & Knuckles"

The music that was in the Mean Bean Machine/Puyo Puyo boss fight was the 2 player theme from Mean Bean Machine / Satan's Theme in Puyo Puyo

*1 day later after sonic mania was out* DAYUM PEOPLE ALREADY FOUND EASTER EGGS

On the first scene in sonic mania, when the robots used chaos control, the sound of the gem is the same sound in sonic forces trailer. When infinite uses his power to summon the the purple glowing cubes.

This video was great! & Knuckles.

They added the debug mode cheat through sound test. Pressing Y+B on the title screen (on Switch) brings you to to the Level Select screen, which also has a Sound Test option. Entering 01 09 09 01 00 06 02 03 and then a level activates Debug Mode. This is a reference to Sonic 1, where the same method is used for Debug mode as well. As for the numbers, it's a reference to when Sonic 1 was released in Japan.

25 sonic mania Easter eggs you might have missed & knuckles

The trailer also has an Easter egg in it. The elevator that Sonic Tails and Knuckles are in during the begininning show the floors - 1, 2, 3, K, M. This is referencing Sonic 1, Sonic 2, Sonic 3, Sonic and Knuckles, and Sonic Mania.