Cictern Stalker

Deathtouch
Whenever another nontoken creature dies, put a +1/+1 counter on Cistern Stalker.
At the beginning of your upkeep, if Cistern Stalker has four or more +1/+1 counters on it,
each opponent loses X life where X is half the number of +1/+1 counters on Cistern Stalker, rounded down.