From Dark and Darker Wiki
If you don't kill the summoned skeletons in time on high roller the boss will enrage/frenzy buff them. This massively increases their movespeed and they glow red (I assume it gives a damage buff too but never got hit)
He also summons an area denial circle of the same color as the purple targeted ring around the room, if you're inside the purple glow/animation it does slow damage ticks (think staying in the gas as the map circle shrinks)
On high roller you either plant pavise's to run the void seeker (purple orb that follows you) into or you run to one of the 8 room exits and angle it so it explodes on the wall as it curves.