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 - $23.50
Lightly Played - $21.20
Played - $16.50
Heavily Played - $14.10
Damaged - $11.80
Near Mint Non-English - $23.50
Lightly Played Non-English - $21.20
Played Non-English - $16.50
Heavily Played Non-English - $14.10
Damaged Non-English - $11.80