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 - £17.80
Lightly Played - £15.10
Moderately Played - £12.50
Heavily Played - £8.90
Damaged - £5.40
Near Mint Non English - £17.80
Lightly Played Non English - £15.10
Moderately Played Non English - £12.50
Heavily Played Non English - £8.90
Damaged Non English - £5.40