Mythics are really just more damage everywhere. There are a few fights that have like, one new ability, but I couldn't tell you which ones: I'd notice it vaguely as a healer or tank and that was only because I was like, Oh what the hell is doing all that damage to me? I don't think I've seen this dude do that before. Oh it's a mythic thing, but it's his normal shit that is doing that much damage.
I absolutely hate grimrail docks; I dunno what those retards were thinking with those packs in the train cars. 4-5 pack, every dude does a cone AE, floor effect AE, etc, so if you have DBM it is a nonstop BEWARE, BEWARE, BEWARE. And because it's such a tiny area, there's nowhere to go. Pop a cooldown and pucker up. It's the one mythic I prefer my DK in, since I use remorseless winter. (Stuns mobs around me after a few seconds.)
So if you're not super geared, just take the pulls slightly slower. I'd have liked to use CC while learning them, but between hunters and just trigger happy DPS in general, a CC won't last.
Clicking off misdirect/ToT when a rogue or hunter tries to pull for me and watching them die is my favorite thing though.