ID please.coral?

[Madreefer]

Looks like some kind of a leather and those things taking over your rocks look like clove polyps. I had them in my tank and they took over everything. Got to the point that I wanted to take my tank down. Good luck with them and hopefully they're not as evasive in your tank as they were in mine.

[Magickiwi]

Leather coral and possibly clove polyps although they may be glove polyps. I have glove polyps and they don't grow for me. Leave them be for a bit and see what they grow up into.