When Green Farm enters the battlefield, sacrifice it unless you pay .
: Add or to your mana pool.
Put Green Farm on top of your library: Add to your mana pool.
: Green Farm becomes a 2/2 white Knight creature until end of turn. It's still a land.
.
: Add or 
to your mana pool.
to your mana pool. : Green Farm becomes a 2/2 white Knight creature until end of turn. It's still a land.
