L13E1: Remorhaz 

It is criminal that your high-quality content doesn't get more attention, I watch every video!

Just before my next session! Let's GOO!

Level 13 let's go! The Fighter has been switched up, she did well but it was a pretty tough fight (especially for a melee combatant), a pretty significant amount of resources were used here. I'm looking forward to the next episode, take care all.

This has been a great series. I would love to see a version of this with fully customized builds as well someday.

Our DM threw one of these at us when we were lv 7 with 5 characters. First hit was a surprize attack on my buddy, Mania who is a whacky Orc Artificer. And it was a crit. Poor guy took like 60ish HPs worth of damage and only clung on due to some ability to remain at 1hp. My Monk launched into an attack using Booming Blade, sword strike, and Bonus Action Booming Blade. She moved 30 feet to try and provoke an Opportunity Attack but Rob our DM was too smart to use his reaction because that meant dropping Mania to attack me which is what I was going for. He knows my tactics all too well... haha! Im the big distraction. I was also surprised by the Heated Body feature but got around that with Absorb elements and absorbed the rest with Bastion of Law 5d8 damage reduction. No concentration for checks for haste needed.

I'd politely make my case to you, the DM, that burrowing does in fact provoke an attack of opportunity. An opportunity attack occurs right before the target leaves your reach (PH, 195). Jeremy Crawford. That means the instant your enemy starts to move you get to slam it with an OPA. Its not when you have left, which would afford you concealment, its right when you left thats the trigger. An example would be my Shadow Sorcerer moving away from an orge to the next space that affords me total cover. Once I move from the space, the two flanking orges get OPAs against me at advantage (if youre using that OP rule) because the advantage was gained at the square I left and not the square that provides total cover. So the Rehmoraz triggers the hit right when it starts to dive into the ice to melt through, not when its already in the ground. I would say anytime you run into a mechanic that allows you to attack in melee range without retaliation unless under very particular circumstances like disengaging, or the Swashbucklers Fancy Footwork, or being blinded/the enemy being obscured, something might be wrong. The developers really stray away from those kind of features unless there is some expenditure in reasources and having the right skills - ie Invisibility grants you offensive/defensive abilities but doesn't make you COMPLETELY immune to being targeted without ready actions - it stops certain spells that require sight and OP attacks but not attack rolls even if its at disadvantage. If you have to ready an action just to fight a monster, something is probably off. The dev team typically stays away from that kind of tactic. Whoopie! I found one small ruling thats not RAW/RAI out of several videos. Of course this is your world your rules, but id at least point out the spirit of the rules according to the developers.