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 - $23.60
Lightly Played - $21.20
Moderately Played - $18.90
Heavily Played - $16.50
Damaged - $11.80
NM-Mint Non English - $23.60
Lightly Played Non English - $21.20
Moderately Played Non English - $18.90
Heavily Played Non English - $16.50
Damaged Non English - $11.80