(Overgrown Slagheap isn't a spell.)
When Overgrown Slagheap enters the battlefield, sacrifice it unless you pay 1 life.
Red creatures get +2/-1.
: Add or to your mana pool.
Put Overgrown Slagheap on top of your library: Add to your mana pool.
: Add 
or 
to your mana pool.
to your mana pool. 
