When Tree Den enters the battlefield, sacrifice it unless you pay 3 life.
: Add or to your mana pool.
Sacrifice Tree Den: Add or to your mana pool.
: Tree Den becomes a 2/2 green Snake Stag creature until end of turn. It's still a land.
: Add 
or 
to your mana pool. or to your mana pool.
: Tree Den becomes a 2/2 green Snake Stag creature until end of turn. It's still a land.
