Sans, Snowdin Sentinel

When Sans, Snowdin Sentinel enters the battlefield, you gain 1 life for each creature card you have destroyed. Sans gains +0/+1 for each creature you Spare. (Instead of destroying a creature, you may return it to it's owners hand. If it reenters the battlefield, it can't attack.)
If you continue destroying creatures, you may keep your extra life. If you start sparing creatures, you lose that life.
Papyrus, you want anything? -Sans