Successfully complete the game on the easy difficulty setting with Aquaman to unlock Classic Aquaman. Classic Aquaman has no Morphing Claw, which means some of his combo moves are not available. However, he swims slightly faster and his telepathy call is different.
Successfully complete the game on the easy difficulty setting with Classic Aquaman to unlock Tempest and Black Manta. Tempast (Aqualad) has less combos than either Aquaman or Classic Aquaman, and no telepathy. However, he has an Ice Beam combo move. Black Manta also has no telepathy power, but has the best combos in the game (some of which require practice). The easiest move to use is the Heat Ray Beam attack or the Grab Heat Ray attack.