It's peppermint shrimp for me. they have destroyed multiple corals and two expensive clams before I figured out who the culprit was. No longer welcome.
Saying that, they are extremely easy to catch, so I add them when needed, but will then catch and get rid of when their purpose is fulfilled.
The same thing that makes them valuable in a reef tank, also makes them dangerous in a reef tank.
They are no longer considered full time inhabitants of my reef, but they are still welcome to come for a visit, but only when invited.
love my urchin and conchs. All model citizens and welcome full time residents.