I removed all mods except Fiend Folio, fps drops to 30 from the amount of tears on the screen.
It is especially noticeable on the final bosses of the last DLC

And when I disable this mod (along with the api), the fps becomes stable, all 60 out of 60, even when ALL the blood clots are firing with me.

Items:
godheaad
Cricket's Head / Body
Sad Onion
20/20

Character:
Spoiled Eve, full health.

Game window size, window resolution, render quality, disabling effects inside the game config do not give any results. Only by disabling the mod completely.