Armagedillo drops Armagedillo's Tail, which is a bind on equip item level 312 two-handed physical dps mace. He also drops around 20 gold (why an armadillo is carrying cash I can only wonder...), and for leveling characters killing him yields a hefty amount of experience.
I haven't done a lot of research on his spawn timer, but I can tell you that he is up quite often because on my route looking for Mysterious Camel figurines I have killed him several times. Often twice in the same day.
Oh yeah, he also breaths fire...
He is also one of five rare spawns found in Uldum. All of them are:
- Akma'Hat <Dirge of the Eternal Sands> - Group Boss, drops a nice epic belt
- Armagedillo (HUGE armadillo) - drops a 2-handed mace
- Cyrus the Black - drops a mail caster belt
- Madexx (Tamable Scorpid) - Spawns in 5 different colors, only drops a tear
- Mysterious Camel Figurine - takes you to Dormus the Camel-Hoarder who drops Reins of the Grey Riding Camel