As Chaos 4, Chaos is more fish-like, differing greatly from its appearance as Chaos 1 and 2. Chaos 4 has a shark-like body with a dorsal fin on both its back and a horn on its forehead, and the flaps on the sides on its head have grown longer. It also has two sharp pelvis fins and a pair arms like Chaos 2's, except its hands look more like fins and lack thumbs. Inside its hands and wrists it has grey bones, each with a Chaos Emerald embedded in them. It also has bones running from its tail fin to its belly where it has a pelvis-like bone holding two Chaos Emeralds.
Chaos 4 has new powers over its previous form, including being able to fire energy waves, swimming at high speeds, creating water explosions by slamming its body on water, and turning into four balls that bounce toward the player. If Chaos 4 is out of water, it simply floats in the air. Chaos also can launch an extendable arm, charged by energy to the opponent as well.
The battle with Chaos 4 is fought over water. Use the lily pads to stay out of the water, and jump immediately if you slip and fall. Chaos 4 attacks if he senses you sitting in the water. Hop around the lake. Chaos 4 uses a variety of distance attacks that consist of multidirectional shock waves. When Chaos 4 stops attacking and pokes his head up, Just as the Chaos before him, Chaos 4 breaks into small pieces, then reforms. Keep out of his way until he pops up, then let him have it.
Chaos 4 is fought over water. Keep Tails out of the pond as much as possible. Chaos 4 attacks quickly when Tails lands. drop on a ring, but jump immediately to dodge Chaos 4's attack. Don't fly farther than you need to, and stick close to Chaos 4. Chaos 4 is temporarily vulnerable when it rises. Quickly land near it and attack. Jump clear when you hit the beast. The reforming energy balls can hurt you. It takes four hits to sink Chaos 4.
Hopefully, by the time you face Chaos 4 as Knuckles, you've seen the Chaos monster's fourth incarnation while playing as another character. Knuckles has trouble getting out of the pond if he falls in. Make quick stops on the lilypads and wait for the monster to peek up. You can land beside Chaos 4 and use Knuckles's punching attack, if you're willing to risk getting hit. Alternately, ball up and drop on the monster from above. You have to score four hits to sink the beast.
In the anime series Sonic X, Chaos 4 appeared during the Chaos Saga. During a battle between Sonic and Dr. Eggman, Chaos 2 snatched their Chaos Emeralds to become Chaos 4 before fighting Sonic. Although Chaos 4 had the environment advantage, it still lost the battle. It later appeared on the Egg Carrier where Eggman made it into Chaos 6.