Sorry that's not it either. I suppose I should give a clue. The title of the episode is the name of the main villain featured in it.
It is! I was scrubbing through it looking for a good shot, and had completely forgotten that this was how the Mutants infiltrated the Lair.
It was honestly purely a wild guess. I had no idea from the shot what episode it was. I just thought of the few episodes in which Mutants enter the Lair and Wolfrat was the first one that came to my mind. Sticking with the Mutants theme, here's another one of them: