Delve mechanics

First can the unspawnning fungus that they fixed not respawn so many times in Fungus Folly. 2 mechanic I cant find answers to, first my screen starts to go gray and quickly kill me, cant find any info on what this is second i get hit and then 90% of my health is grayed out leaving me with a lil 10% health block. Ive tried looking this up and cant find any info, any help be appreciated

It’s kind of funny how easy folly is but the fungal respawns on last boss actually makes the boss a bit harder than other bosses.