(victory)
DM: And, at long last, combat is complete. You are the only "you"s left standing.
Fluttershy: I think I'm kind of combat-ed out now. Anyone else?
Rarity: Agreed.
Pinkie Pie: I dunno, I could go for a few more rounds of uninterrupted butt-kicking!
Rainbow Dash: Nah, I'm with Fluttershy. That was enough gimmicky combat for one session.
DM: Yeah, this concept needs a post-mortem. Thanks for sticking with it, though.
Applejack: Ah didn't want to bring this up in the middle, but why didn'tcha use the swarm rules?
DM: *...D'OH!*
Sometimes even a bad idea is fun once. I once ran a large scale battle where the players had to martial dozens of NPCs to defend 5 separate locations from simultaneous attack. They had players on several different maps in Roll20 communicating telepathically. I had to switch maps every time a new player's turn came up. It was epic, and huge, and took 4 sessions to finish. We all had a great time and agreed to never do it again :p
Unless you're doing a campaign path with set story checkpoints to level up to keep up with the pre-calculated encounters, it doesn't really matter when the players level up except that it should happen at a moderate pace. XP works just fine for that.