OXM - Like Lilith from the first Borderlands, Maya is one of the world's six Sirens - ladies with ace supernatural powers. Her Phaselock skill lets her freeze foes in time, making her the most suited to co-op games of all four Borderlands 2 characters.
Hoisting the most dangerous enemies into the air and preventing them from fighting back can turn the tide of battle, and there are optional upgrades that make things even more useful. The Helios skill in the Cataclysm tree transforms Phaselock into an inferno, causing explosive damage to all foes nearby. Invest heavily in the rest of the tree, and you'll evolve into a walking natural disaster of fire and acid.