Power Crystal

Power Crystal enters the battlefield tapped
Put two charge counters on Power Crystal on
your untap step
{t}: Remove X charge counters from Power
Crystal: Add X colorless mana to you mana pool.
{t}: Remove XX charge counters from Power
Crystal: Add X mana of any color to your mana
pool
When Power Crystal has twenty or more charge counters on it, destroy all creatures and Exile
Power Crystal.
.