I find the Thunderhead one on CM is kinda annoying since the boss just dash all day long (then do some annoying 2 chain knockdowns wherein the 2nd hit is actually 2 hit - lifting wing/arm then shockwave). The lifting wing/arm one is hard to time since the moment it gets lifted, anything within melee range is instantly knock downed. If u do dodge it, u get hit by the shockwave next unless double dodge. The Block is a bit tricky too since the adds can remove it. I'm guessing stab is the way to go but the damage hurts too.
Another thing to point out in Thunderhead is the color of the environment + the AOE circles and fire. If the boss manage to stay in the middle near the forge, you need very very GOOD EYES to differentiate between where is the fire and which is the ORANGE AMBIANCE COLOR. Same goes with the small little destroyer crabs in the sea of adds if it goes hectic.
On a different note for the Thunderhead, anyone manage to understood how the dash targetting on the boss work? or is it fully random? My last attempt on running it solo, i manage to make it ping pong on the side pillars. But I kinda can't replicate it anymore since it always charges to anywhere it wants.
Haven't tried CM on Snowden so can't really give a thought about it,