- The Fox and the Cat in the opera The Adventures of Pinocchio definitely qualify. Although a bit bumbling, and definitely comedic, their scenes can be intensely creepy. And also a bit something else. They might not kill anyone outright, as they're rather poor at their jobs and more tricksters than assassins, but they certainly make a good try at it. (Such as trying to lynch Pinocchio for the five gold coins he got out of sympathy from the puppet show owner.)
- Rosencrantz and Guildenstern of Hamlet and Rosencrantz and Guildenstern Are Dead fame counted — they might not be straight up villains in Hamlet but they definitely qualify.
- A few William Shakespeare cases, especially the two killers sent after Clarence in Richard III, and Chiron and Demetrius in Titus Andronicus.
- The Dumb Waiter is all about Those Two Bad Guys.
- The First Man and Second Man from Kiss Me Kate don't kill anyone on stage, but they are mobsters and they talk an awful lot.
- Kurt Weill's opera Die Bürgschaft has a recurring trio of nameless villains who adopt New Jobs As The Plot Demands.
- Goldberg and McCann in The Birthday Party.
- Jessie and James in Pokémon Live!.
Those Two Bad Guys / Theater