I've noticed the concept of swarm (there called "clones") in Badland, and I've never seen anything like it. Here's a video showing it.
I'll describe it:
- you start with one guy, and going on through the level you may "pick up" new guys, which are exactly like the one you already have (there's no "main" one, they are indistinguishable)
- you can't control them individually: your actions are applied to them all
- you may lose a few of them along the way, and you "die" if you lose them all
This is very different from Lemmings, were you control the single guys.
At most it could be considered somewhat similar to Cannon Fodder (or Syndacate or some RTS), but even there you had the ability to control a single guy: crowd movements were only a convenience were "it did not matter" to control specific individuals. Here you are forced to control them all together and this is a core feature of the game.
Someone could argue that Pele's Soccer had a similar movement system, but it doesn't have the concept that you could lose some guys and go on (and maybe pick new ones), and anyway it's not a core feature of the game, it's just a simplification due to the capabilities of the console.
Patapon could be considered to have a similar mechanic, but AFAIK being it a rhythm game you don't really get to chose what to do, unless I'm mistaken (I never got to play it).
Games were you have random sidekicks don't really count, since they are very different from you: usually when you get hit you die (like in shooters), or they are just a "second chance" but they almost aren't part of the game as long as they are in the background (like in Donkey Kong Country).
So, is this a novel idea, or did I miss something?