Iracog, He Who Bears Many Scars, was a legendary regeneration-bugged water buffalo bull. This object menaced with spikes of embedded arrows. On this object was an image of the gates to the afterlife in water buffalo horn.
I pastured some animals outside as an early warning system for a Fortress Defense fort, expecting total animal annihilation once the sieges hit. Most were easy goblin and strangler bait, but Iracog was not like the others. While he possessed the mind of a normal water buffalo and would attempt to flee from invaders, his body could not die in battle. Remember this was Fortress Defense. Iracog survived outside for many seasons, fleeing from enemies and kicking them to death one by one as they approached from behind. His spine eventually broke, but this merely caused Iracog to spend less time running from enemies and more time kicking them in the head very, very hard. Every wound healed before he could bleed to death. It is speculated that this is caused by the RNG choosing healing rates on a bell curve, and Iracog was way out there on the curve leading to anomalous Highlander livestock.
Iracog was never properly killed. The overseer foolishly placed him inside, away from grass to munch and blood to drink, and Iracog starved to death in a meeting hall while waiting for his temple to be finished.