When Unstable Hollow enters the battlefield, sacrifice it unless you pay .
: Add or to your mana pool.
: Unstable Hollow becomes a 2/2 red Shaman creature until end of turn. It's still a land.
.
: Add 
or to your mana pool.
: Unstable Hollow becomes a 2/2 red Shaman creature until end of turn. It's still a land.
