His dominant element is lightning, however he controls all four powerfully. There are only four golden weapons because each only controls one element. The Megaweapon is kind of like a fifth golden weapon, as it is a combination of the Four. But Lloyd doesn't need an elemental weapon, because the elemental powers are already in him. The other four Ninja needed the weapons because the elemental powers weren't inside them- they were in the weapons. Lloyd, as a direct descendant of the First Spinjitzu Master, and having been chosen by the prophecy as the Green Ninja, already has the powers inside him.