The only real skill to watch out for is when he encases a player in a light-blue gloop stone. It completely immobilizes you, like the Demon Grasp from the last boss in HoDL, and the bubble cage from Paicha in RT.
Think of the last boss strategy in DoD. He places a dark cloud on a patch of ground with purple tendrils pulsating through it. Players caught in the dark cloud must move away, as it puts a DoT and slows your casting speed.
She places a purple skull debuff on a random player, making it so that while the debuffed target it near her, it will heal her. The way to get rid of this is for that player to run to the back of the arena and wait for the debuff to disappear - it only takes a quick moment. Be sure to keep running, because she can teleport you back to her. An unconfirmed strat is to cleanse the debuff off.
At certain points he spawns clones of himself, and at that time the real boss is unable to be damaged. The clones must die first - and it's useful to mark the real boss before the fight begins.
Infected Dreamland Guardian
My memory is still a little hazy on how exactly this boss will react. From what I remember, he spawns un-killable adds that need to be ignored. All dps should only focus on killing the boss, and the healer should be able to out-heal the damage the mobs are doing.
Nightmare Beast Atollop
From what I've seen, he does a few things the previous bosses have done. He spawns the dark clouds beneath players like in lv10, and I believe he also spawns adds that cannot be killed. Big dps race here, not sure what happens the longer the fight goes on. Still need to confirm a few things.