(Grass-Necropolis isn't a spell.)
Grass-Necropolis enters the battlefield tapped.
Green creatures get +1/+0.
: Add or to your mana pool.
: Add to your mana pool. Put Grass-Necropolis on top of your library.
: Add 
or 
to your mana pool.: Add 
to your mana pool. Put Grass-Necropolis on top of your library.
