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.)
"Hup, two, three, four, Dunno how to count no more." —Mogg march
Near Mint - $33.80
Near Mint Non-English - $33.80
Lightly Played - $30.40
Lightly Played Non-English - $30.40
Played - $23.70
Played Non-English - $23.70
Heavily Played - $20.30
Heavily Played Non-English - $20.30
Damaged - $16.90
Damaged Non-English - $16.90