I see mesenterial filaments (inner distended tissue of your coral) and an asterina starfish. Ultimately, I think there’s more fear mongering on asterinas and mixed opinions. “If they have a red or orange dot(s), they’re not reef safe.” I never could tell I had any problems in my first tank and I had a healthy population of these guys. But I don’t think I ever let them annoy my corals when I saw it….
Tldr: probably safest to pluck it off! Especially if it came with the coral. “Where the food goes* I go”