So this word fungus popped up in a pot of diffenbachia, overnight. Has anyone ever seen this stuff.??
Button mushrooms. Pull them out before they set millions of spores. Harmless to your plant (feeding off dead organic material) but don't eat any without knowing what is toxic and what isn't.
Look more like puffballs, also a "mushroom." They like growing in mulch/bark and such, like these are. Just leave them alone or take them out and toss them if you don't like the way they look. They'll disappear in a few days.