Each creature gets +1/+1 for each other creature on the battlefield that shares at least one creature type with it. (For example, if two Goblin Warriors and a Goblin Shaman are on the battlefield, each gets +2/+2.)
Near Mint - $24.30
Lightly Played - $21.90
Played - $17.00
Heavily Played - $14.60
Damaged - $12.20
Near Mint Non-English - $24.30
Lightly Played Non-English - $21.90
Played Non-English - $17.00
Heavily Played Non-English - $14.60
Damaged Non-English - $12.20