Greth, Soulless Conqueror

When Greth, Soulless Conqueror enters the battlefield or attacks put a -1/-1 counter on each creature you control.
Whenever a creature you control dies put a +1/+1 counter on Greth, Soulless Conqueror.
{3}, Pay 3 life: Exile a creature card in any graveyard to put a +1/+1 counter on Greth, Soulless Conqueror.