Something that popped in my head was the idea of swarms as followers and we already have a rat model as is. So here is my idea.
Rat Swarm. You can get a rat group of 3 rats/open follower. Each of these rats start with 100 hp at level 1 with an attack of 20. The group of rats can regenerate rats slowing as long as they have at least 1 rat in the group (you have to kill all 3 rats to kill the follower). The group attacks one enemy at a time but can be attacked by multiple (the group acts like any other follower in that they focus on one but can get ganked) Like zombies, you can have 3 groups of rats and therefore a total of 9 rat followers (or 12 if you got war party).
This can be applied to other small creature pets in the future (bats, ravens, scarabs etc) but since the rat model is here, it is the easiest to get going.
I would have this either as a purchased pet at a vendor or, more appropriately, additional levels of sorcery allow you to either summon or create whistles/lures to get the pet going.
