Kyuubi is a mob found in dungeons of one of the ant worlds, it is a definite reference to naruto.
Shoots fire balls, most likely a melee move as well
Nether, ant world dungeon
How to kill:
Fire resistant armor or fire proof material
Coal, Redstone, Quartz
Like i said earlier, this is a reference to the popular anime known as Naruto, it is Naruto in his version 1 tailed beast cloak