Nibelheim Reactor

Nibelheim Reactor enters the battlefield tapped.
Upkeep {r} (During your upkeep, sacrifice Nibelheim Reactor unless you pay its upkeep cost.)
{t}: Choose one - Add {1}{b} to your mana pool; or search your library for a creature and add it to
your hand, then shuffle your library.
"Our mission is to investigate an old Mako reactor.
There have been reports of it malfunctioning, and producing brutal creatures."