(Sunpetal Seafloor isn't a spell.)
Sunpetal Seafloor enters the battlefield tapped.
Green spells cost more to play.
: Add to your mana pool.
: Add or to your mana pool. Each opponent gains 1 life.
more to play.
: Add 
to your mana pool.: Add 
or 
to your mana pool. Each opponent gains 1 life.
