(: Add or to your mana pool.)
Green Cavern enters the battlefield tapped unless you control one or more creatures.
: Green Cavern becomes a 2/1 green and black Stag creature until end of turn. It's still a land.
: Add 
or 
to your mana pool.): Green Cavern becomes a 2/1 green and black Stag creature until end of turn. It's still a land.
