Mistwraith

Whenever a creature you control dies, put a +1/+1 counter on Mistwraith.
"When they find a corpse, they slowly digest the muscles. Then they use what they've eaten as a pattern, creating an exact duplicate of whatever they've eaten. The excrete whatever they don't want, and keeps the ones that they do want, adding it to their body--which forms that jumble of bones and flesh."
-Kelsier to Vin