This is more of a reverse ponies in unusual places, but the same roar got used for both the ursa minor in Boast Busters (S1E6) and the battlelord sentry enemy in Duke Nukem' 3D. After hearing that roar over and over again while playing Duke 3D, I immediately recognized it upon rewatching the episode. Can't get that kind of sound out of your mind with how many of those things scream at you.