(Grave Outpost isn't a spell.)
Grave Outpost enters the battlefield tapped.
Discard two cards: Put a 2/2 black Zombie creature token onto the battlefield.
: Add or to your mana pool.
Put Grave Outpost on top of your library: Add to your mana pool.
: Add 
or 
to your mana pool.
to your mana pool. 
