Putrescent Knight

Trample, swampwalk.
This enters with an additional +1/+1 counter
for each creature card in all graveyards.
Whenever another creature dies, put a +1/+1 counter on this creature.
At the beginning of your end step, remove a +1/+1 counter from this creature.

{1}{u}{b}, Remove X +1/+1 counters: Copy target sorcery you control with mana
value X or less.