Derketh, Sunbleach Sovereign

Convoke, vigilance, deathtouch, lifelink
Derketh enters the battlefield with a +1/+1
counter on it for each Skeleton that convoked it.
Whenever a Skeleton you control becomes
tapped, put a +1/+1 counter on Derketh.
{w}{b}, {t}: Remove all counters from Derketh.
Each opponent loses X life, where X is the
number of counters removed this way. You
gain life equal to the life lost this way.