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."
Near Mint - $22.80
Lightly Played - $20.50
Played - $15.90
Heavily Played - $13.70
Damaged - $11.40
Near Mint Non-English - $22.80
Lightly Played Non-English - $20.50
Played Non-English - $15.90
Heavily Played Non-English - $13.70
Damaged Non-English - $11.40