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 - £18.20
Lightly Played - £15.50
Moderately Played - £12.80
Heavily Played - £9.10
Damaged - £5.50
Near Mint Non English - £18.20
Lightly Played Non English - £15.50
Moderately Played Non English - £12.80
Heavily Played Non English - £9.10
Damaged Non English - £5.50