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 - $14,900
Lightly Played - $11,900
Moderately Played - $10,400
Heavily Played - $9,000
Damaged - $7,500
Near Mint Spanish - $14,900
Lightly Played Spanish - $11,900
Moderately Played Spanish - $10,400
Heavily Played Spanish - $9,000
Damaged Spanish - $7,500