Druidium Reactor

When Druidium Reactor enters, you get {e} (an energy counter).
{1}, Sacrifice a land: Search your library for a land, put it onto the battlefield tapped, then shuffle. You get {e}.
{2}, Sacrifice Druidium Reactor: Create a 5/5 green Elemental Mutant creature token with persist and
"At the beginning of your end step, sacrifice Elemental Mutant unless you pay {e}{e}".