Black explosion effect?

Hi exiles

Lately I've been dying to a one shot mechanic in t15 maps that I cant figure. It is not corpse or fungus explosion or the dots we know. It is just one shotting my full life char and all I can notice is just a very little black splash under my feet, after it is too late ofc. Any idea which monster mob or mechanic cause that?

I'm playing fairly careful so I just wanna know at least what it is. I'm an active block titan max res, 44 chaos res, %85 pshy reduction.