What is this big grey bubble on my hammer?

[Steve1500]

Any ideas and advice on what this is?

 

[PicassoClown04]

Maybe a polyp bailout situation? Sometimes a polyp does this and a new head comes out of it! Never had this happen to me tho, someone else might know a little bit more

 

[BighohoReef]

They do that from time to time, it can be bailout, but I've had it happen on a few euphyllia. Some might say growth but normally that's showing the stringy brown stuff they excrete. I'd just watch it... it'll go down in a few hours or less