Eldrazi Harbinger of Despair

When Eldrazi Habinger of Despair enters the battlefield you may reveal an Eldrazi card from
your hand, that card cost {x} less to cast where X
is equal to target creatures power.
If you don’t control any other creatures, this creature gets +2/+2.
~A path of death and destruction in their wake. We
thought the worst had passed, we were wrong.