Definitely a mantis shrimp. You may here clicking coming from the tank, and will start losing hermits and snails. Many of us have had mantis only species tanks. I agree the 'star' is a tube worm, and the ??? does look like a majano anemone which will take over and wreak havoc. I would do some research on the mantis, if you don't want it, somebody will. Also research the majano, I would try to kill it in place, that rock is darn nice to nuke.