Ah Puch

Ah Puch is the Mayan god of death and protector of the Sword of Ekchuah, Ah Puch is even larger than Fourarms (about twice as large) and strong enough to send Fourarms flying with his tongue alone. He appeared in Ultimate Weapon. He first appeared attacking The Forever Knights as they attempted to steal the sword. He was largly winning against them, but attacked Ben and company when they tried to reach the sword. He was defeated by them, and left in the temple as it collapsed; what became of him is unknown. Though he attacked Ben and the others, he only did so to defend the sword. His image was used for the Mask of Ah Puch, the only thing that could lead one to the sword.

It's possible he's an ancient alien that primitive human beings began to worship.

Powers and abilities
Ah Puch is an ancient alien, has incredible super strength and superhuman durability. He easily defeats a small faction of Forever Knights and later just as easily pummels and physically overpowers Ben in his Fourarms form, literally tossing him around like a ragdoll. It wasn't until Ben saw his family in trouble that he managed to muster the strength to defeat Ah Puch and even then, a powerful punch with all four of his arms only stunned Ah Puch for a few seconds.