Centaur Flats enters the battlefield tapped unless you sacrifice a Specter.
: Add or to your mana pool.
Put Centaur Flats on top of your library: Add to your mana pool.
: Return Centaur Flats to its owner's hand.
: Add 
or 
to your mana pool.
to your mana pool. : Return Centaur Flats to its owner's hand.
