When Horizon Seafloor enters the battlefield, sacrifice it unless you pay .
: Add or to your mana pool.
: Horizon Seafloor becomes a 2/1 white and blue Citizen creature until end of turn. It's still a land.
.
: Add or 
to your mana pool.: Horizon Seafloor becomes a 2/1 white and blue Citizen creature until end of turn. It's still a land.
