The tiger striped or aka banded serpent star is by nature a predator star. They can be a concern with small unaware fish, so keep tabs on it
They are however great scavangers and will benefit the tank in many ways. The best way to keep it happy is by feeding it. A small raw piece of seafood weekly should do the trick. Krill, shrimp silversides, whatever you have available. They aren't terribley picky.