Character: Sonic, Tails, Knuckles
Location: Mystic Ruins, Red Mountain
Weakness: Head when exposed
Chaos 4 is a larger, more powerful form of Chaos, fought in a flooded arena. As Sonic, you'll need to run across the water's surface to reach him. Chaos 4 will create large waves and occasionally submerge. When he creates waves, jump over them. When he surfaces, his head will be exposed. Use a Homing Attack to strike his head. He may also try to suck you in; run against the current to avoid being pulled into his mouth. As Tails, you can fly above the water, making it easier to avoid his attacks. Fly towards his head and use your tail whip when it's exposed. As Knuckles, you'll need to glide and climb to reach higher platforms to get a good angle on Chaos 4. When he surfaces, glide towards his head and punch it. For all characters, the key is to avoid the water-based attacks and strike his head when it's vulnerable.
While Chaos 4 requires navigating a flooded arena, Sonic Forces reimagines this entity as an illusory boss encounter that emphasizes high-speed platforming and quick-time events.
While Chaos 4 requires running across water to attack, Sonic Frontiers evolves this aquatic mobility through the more expansive open-zone traversal mechanics found on Ouranos Island.