Karn, Successor of Yawgmoth

Indestructible
As an additional cost to cast Karn, sacrifice two creatures.
When Karn enters the battlefield or leaves
the battlefield, distribute X -1/-1 counters on
any number of target creatures where X is the
number of Artifacts you control.
Whenever you cast an Artifact spell,
if you control three or more Swamps or
or three or more Artifacts, put a poison counter
on target player, then proliferate.