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."
Near Mint - $15.500
Lightly Played - $12.400
Moderately Played - $10.900
Heavily Played - $9.300
Damaged - $7.800
Near Mint Spanish - $15.500
Lightly Played Spanish - $12.400
Moderately Played Spanish - $10.900
Heavily Played Spanish - $9.300
Damaged Spanish - $7.800