The Abyss initially appears alone in battle in the Double Reed Tower of Sand and later in groups of two or three. It also sometimes appears alongside one or two Steam Horns. In the darkness, it morphs into the Black Onyx.
The Abyss's normal physical attacks are jabs with its arms. Implosion is a popping middle-distance attack that hits all targets in range. Dark Sun deals damage to a single target and carries a chance of Darkness Body. Left Blow, Left Drill, Right Blow and Right Drill are all the same basic attack, three hits with a chance of knockdown, though the chance for knockdown is greater with some than others.
The Abyss has somewhat high defense, but is otherwise a relatively non-challenging opponent for this stage of the game, and certainly much less dangerous than its dark Black Onyx counterpart. It has several different attacks that can do three hits of damage on a target, but all are weak and easily Guarded against. The only thing to watch out for is the Dark Sun attack that causes Darkness Body, so if this happens, move that character out of the way if you'd rather not fight the Black Onyx. Otherwise, this opponent will easily fall at this stage of the game using standard tactics.
- In the PlayStation 3 version of Eternal Sonata, this opponent's HP was decreased by around 7000 points, while the EXP granted for defeating it was reduced by a little less than half.