The life of a creature within Kuldra's Tower is not a pleasant one. Every beast or warrior (even the undead ones) are at constant threat from any of Kuldra's five heads, and the tower itself is a font of anima. Any kind of life expectancy is a luxury.
Evolution has handed the creatures of Kuldra's Tower something of a lifeline. Anima attaches itself to the creatures in a kind of symbiosis. The anima seeps into the creature, feeding on its softer tissue and leaving something like a crystal residue behind. This discordant symbiosis makes the creature hardier, at the cost of a humming, constant pain.