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 - £19.40
Lightly Played - £16.50
Moderately Played - £13.60
Heavily Played - £9.70
Damaged - £5.90
Near Mint Non English - £19.40
Lightly Played Non English - £16.50
Moderately Played Non English - £13.60
Heavily Played Non English - £9.70
Damaged Non English - £5.90