Envy didn't move, slightly put off that Sloth wouldn't let him intervine. He wanted to take a hit. Yet, the longer he stood there he got to witness how Sloth worked.
"Enjoying yourself?" It wasn't really a question as much as it was a prod. Sloth was tapping into that dark side, maybe he had sparked it the other night. Being good was never in Envy's charm. He wanted the worst and Sloth was digging deep.