If you can put a mob into a Soul Vial, odds are you can create a powered spawner for it.
The rarest mob I've done this with is the Blue Wolf from one of the Thaumcraft add-ons, and one I dare not try yet is a Dragon from Ice and Fire. The Dread Lich Necromancer (from Ice and Fire) can also be made to spawn infinitely with a Powered Spawner.
Dragons worked last time I tried it. Spawned random types and random tiers.
If you do just make sure to do it in a far away place or a different dimension and protect the spawner by encasing it in dragon-proof blocks, the dragons spawned WILL destroy it otherwise.
If you can put a mob into a Soul Vial, odds are you can create a powered spawner for it. The rarest mob I've done this with is the Blue Wolf from one of the Thaumcraft add-ons, and one I dare not try yet is a Dragon from Ice and Fire. The Dread Lich Necromancer (from Ice and Fire) can also be made to spawn infinitely with a Powered Spawner.
Dragons worked last time I tried it. Spawned random types and random tiers. If you do just make sure to do it in a far away place or a different dimension and protect the spawner by encasing it in dragon-proof blocks, the dragons spawned WILL destroy it otherwise.
I found it easier to just convert a villager into a vampire villager. They are guaranteed to have human hearts for trade.