The Power Stone

The Power Stone does not count as a card in your
deck.
At the beginning of the game, exile The Power
Stone from your library face down.
At the beginning of your end step, if
the sum of the powers of all creatures you control is equal to or greater than 15, put The Power Stone face up onto the battlefield under your control.
{1}{t}: Sacrifice The Power Stone: Put a +1/+1 counter on each creature you control and a loyalty counter on each planeswalker you control, then proliferate three times.