The Aeorian Reverser made it’s first appearance earlier this season in the Coliseum. As a DM this monster was a blast to run. It has the strength to take a bit of a beating, it can dish out damage in melee combat, and that a Reversal ability? Chef’s kiss!
Preventing healing is already nasty business, but turning it into damage, that’s just brutal! It denies the party’s frontline the support they desperately need to protect the group. The damage turns the best efforts of their allies into a new threat. It both frustrates support and turns it into a threat.
What about when a player goes down though? We go from hurting instead of helping to automatically failed death saves. For me, that makes them ideal for the Coliseum, as the players all know a swift death is on the table. I’d be really hesitant to employ these heavily in a less combat-focused game though. Extra failed death saves dramatically reduce the chances of a player recovering. That said, the drama that a character on the edge of death creates in combat is great, if that’s your game’s speed.