On idea that I think would be nice. If there was a "Spawn monster" spell
basically, cast a spell and then make a rat, Tefusang, Clacker, Trepor or whatever appear just a few feet from you. Doesn't matter if it's friendly or not, just being able to create something like that would be nice.
Imagine this, a mage can summon rats by using MP, a sizable amount so you can't summon a rat every 5 seconds but enough where a high-level character could create about 2 or 3 before having to recharge . These are just regular rats and anyone can kill them with little trouble. Then they can summon them near some new players so the new players can practice on them. If they summon a rat in town, its only natural that someone will kill it in a short time so it won't cause too much lag if lots of people summon rats. The rats will just get killed off. These rats would also have lootable items on them, it would be nothing major and a bit more interesting than just standing in the sewers waiting for rats to spawn naturally.
More powerful monsters might be spawned but they would need more MP, higher levels, and perhaps use up some sort of material. Like to spawn Tefusangs you use up Tefusang Hides, or bits of coal or something.
I know its not really shepherding, but it would supply a way to create creatures to butcher, could be more fun than constantly camping the naturally occuring spawn points. Also it could provide a way for some of them more evil players to cause a bit of RP havok, since monsters can attack players regardless of the "No RvP" option. If wouldn't be too disruptive if the monster once spawned acted just like a regularly spawned monster [i.e. it sits there until someone attacks it, so the caster can't command it to target players. Though with weak rats it shouldn't matter since anyone can kill them]
Anway, thats one idea. I don't think any other MMORPGs allow players to spawn monsters. As far as the herding aspect, if there was a /follow feature, and items like "Rat shepherding staff" or "Clacker shepherding staff" which allows players to make those specific monsters follow them it could work out. Naturally, you don't want staffs that let people lead away all the trepors and rogues and stuff that people use to kill and get xp from. Or lead Ulbernaughts into town with.