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 - $31.90
Near Mint Non-English - $31.90
Lightly Played - $28.70
Lightly Played Non-English - $28.70
Played - $22.30
Played Non-English - $22.30
Heavily Played - $19.10
Heavily Played Non-English - $19.10
Damaged - $16.00
Damaged Non-English - $16.00