Sans, the Skeleton Boy

Sans, the Skeleton Boy enters the battlefield with {x} +1/+1 counters on it.
Whenever a creature dies, put a +1/+1 counter
on Sans.
Wither (Sans deals damage to creatures in the
form of -1/-1 counters.)
"It's a beautiful day outside. The birds are singing, the flowers are blooming... In a day like this, kids like you SHOULD BE BURNED IN HELL!"