This ability counts creatures, not creature types. For example, if you attack with five creatures — an Elf Shaman, an Elf Warrior, a Goblin Shaman, an Elemental, and a creature with all creature types — the ability will trigger five times. Those creatures will get +3/+0, +2/+0, +2/+0, +1/+0, and +4/+0, respectively.