Darth Sion

Whenever Darth Sion dies, exile him and return
Darth Sion to the battlefield at the beginning of
the next upkeep.
Darth Nihilus and Darth Traya gain undying.
Darth Sion gets +X/+X where X is the amount
of experience counters you have.
{b}, Sacrifice another creature: Get an experience
counter.