"Death Dealers" in my reef tank are my yellow and sailfin tangs.
Current ones refused to allow new fish into tank... it was a sad winter. Acclimation boxes that hang on side meant only new fish could live in that meet & greet corner... new fish didn't understand, beat up, went to QT, healed, re-acclimated, eventually died. Repeat. Repeat. Sailfin and mirror - WOW. If it wasn't so hard on sailfin trying to exterminate its reflection, I'd video. Seriously scary.
Got a large SHU OctoAquatics magentic acclimation box that can be moved into different "territories" within my 180g. I credit this acclimation box in being able to return my yellow back to display tank. It didn't do well with Reef Flux and had to 'vacation' (3 week spring break?!) in QT while tank treated for bryopsis.
Pleased to report both my Death Dealers still healthy, happy and at least tolerate each other. Hoping this continues as they continue to grow in size (and aggression <sigh>)