Ziggurat boss question

So I watched tutorials and checked written guides, but I'm not able to find an answer to this:

After I killed the laser beam guy who spawns in the middle of the map and she starts to summon the baby skeletons which I have to kill so they don't develop into full skeletons (from a guide) - the whole inner arena is covered with some DoT floor that I can't outheal. I couldn't find any hints on how to deal with that.

I tried to wait on the side but it didn't go away until I got killed.