Identification: Fungus?

I know that its not a plant, I think it is a kind of fungus.

Its is under my sink, what should I do?

Is it venomous? ;-;

 

To me it looks like some mold growing on bit of expanded plastic foam that has gotten discolored from dampness.

 

I don't think so cause my sink is made of wooden and these things have appeared before.

 

Have you cut it open to see what it looks like inside? That might help with the ID.