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
NM-Mint - $24.50
Lightly Played - $22.10
Moderately Played - $19.60
Heavily Played - $17.20
Damaged - $12.30
NM-Mint Non English - $24.50
Lightly Played Non English - $22.10
Moderately Played Non English - $19.60
Heavily Played Non English - $17.20
Damaged Non English - $12.30