I don't know what this is... coral/critter?

[DAWREEFER]

So, I noticed these kinds of white bulbs popping up a bit back and I took a closer look at it this evening and noticed it's starting to develop neon green. I like to let my tank go all natural and really thought nothing of it when it first started appearing. Now, I'm curious about what it is or if it is harmful to my fish or corals. Let me know, it's pretty neat, to be honest.

 

[Sharkbait19]

Looks like a ball/glass nem (technically a type of shroom). Doesn’t spread like aiptasia so I wouldn’t be too worried, they tend to go away on their own if I’m not mistaken.

 

[PasoFish89]

Looks to me like a ball anemone which is really a mushroom coral like I'm sure someone will have commented by the time I post this haha. Mine tend to open up more at night. Harmless I think, or at least I've never noticed any damage or ill effects.