Tardigrades are microscopic eight-legged animals sometimes called water bears. They are the most resilient creatures on earth. In extreme temperature or dehydration, they shrink into a state called a tun, in which their metabolism practically stops. As a tun, they can survive without water for decades, tolerate high doses of radiation, and are unaffected by temperature extremes ranging from -200 degrees to +300 F.

As wild cards, they have the power to change into any San in their suit.