My serpent star is not small by any means. If I pick him up in my tank his body covers half my palm and he wraps around my hand like a snake, very cool feeling.
Anyway, he climbs all over my corals. Green star polyps, yellow polyps, xenia, and even occassionally moves around my candy cane. I don't move him off because everything he touches just closes up and opens back up like nothing happened just a few minutes later. Serpent stars are awesome and completely harmless. Learn to love them.