Before the introduction of Horde encounters i actually immagined something a little similar
Say you run into a beedrill, but but it's not one, it's an innumerable ammount of them
The difference in this battle, is that the sprite of the beedrill would be just a big bunch off smaller sprites of them, the more damage the "swarm" takes, the smaller it becomes.
The moves the swarm could use would be different, like they all act like a big hivemind, somewhat like some of vespiquen's moves.
Would this be an interesting idea?