The CORE

Flash, Hexproof
This card enters the battlefield tapped
When this card enters the battlefield, sacrifice
any number of lands under your control. Put
that many counters on this artifact
{t}: Add 1 mana of any color to your manapool
for each counter on this artifact.
That's the CORE. The source of all power for the underground.
It converts geothermal energy into magical electricity.