Towards the end of the level Desert of the Knaaren, Reflux finds Rayman and challenges him to a duel in the arena. Gumsi, the child-king of the Knaaren, mentions that Reflux is his "champion" and that he has never fallen to another warrior before.
First fight: Boss of the Destiny Arena
The fight takes place in a small arena, surrounded by a lava pool, with grabbable nets on the sides containing Red Lums and Heavy Fist powerups. He can be defeated by attacking his scepter, but only when he is in the process of summoning yellow orbs. It is recommended that you grab the Heavy Fist powerups at the bottom of the arena to deal extra damage. During the battle, he attacks Rayman using his scepter, which presumably allows him to use the power of the Leptys (though to a limited extent).
After Rayman defeats him, Gumsi berates Reflux for his failure, and grants Rayman the ability to Grimace. Rayman will not need to worry about other Knaaren from this point on.
Later in the game, André is finally freed from Globox's body, and he immediately flies off to recruit Reflux as part of his efforts to defeat Rayman. Reflux, happy to oblige, steals Gumsi's Scepter and meets André at the top of the Tower of the Leptys. He is fought as the final boss of the game through 4 phases, using the power of the Scepter to call on the Leptys.
Final Fight - Phase 1
In his final fight, he appears to have swallowed Andre, though this is likely a symbiotic relationship. He starts by putting up a magical Knaaren shield (that is impregnable to regular attacks) and starts attacking Rayman with surprisingly quick lightning bolts, but changes his strategy once Rayman obtains a Lockjaw powerup. Rayman should target and attack the shield with a Lockjaw while dodging yellow bolts of energy that are fired from the scepter. When the shield is disabled, Rayman needs to obtain a Heavy Fist powerup and attack Reflux in a brief window. After repeating the process enough times, Phase 2 starts.
Final Fight - Phase 2
Reflux, angered at his defeat, takes his Scepter, stabs it into the back to embed the bulb in his flesh, and flings the stalk away. He then grows to an enormous size and punches Rayman out of the arena, also causing the sides of the arena to crack and raise.
Rayman needs to travel around the edge of the broken arena to find a Lockjaw. He needs to hide in the depressed portions of the arena if Reflux swipes at him horizontally, or jump off the ground when Reflux punches the ground- if Rayman is caught on the ground, he will be flung into the air, and while falling, Reflux will attempt to swipe him unless Rayman activates his helicopter. After he completes one circle, Reflux attempts to punch the side of the arena directly, but loses his strength; Rayman should obtain the nearby Heavy Fist powerup and run up Reflux's arm to attack the glowing orb in his back. If the player is efficient, this phase can be completed in just 3 rounds, though Reflux's attacks get faster and more erratic as the battle continues.
Final Fight - Phase 3
Reflux then causes himself, and the surrounding platforms, to float into the air, towards the strange starry formation in the sky. He will not directly attack Rayman in this phase. Rayman must grab a Throttle Copter powerup and begin climbing the floating platforms. However, he must be quick, as the platforms magically disappear after a short time, and Reflux will attempt to blow Rayman out of the air with an electrical ranged attack. At the top, Rayman finds a Shock Rocket, which automatically maneuvers around Reflux and deals a final blow to his glowing orb. Seemingly defeated, Rayman gloats at his victory with a Grimace, only to watch as Reflux sprouts wings and flies into the starry formation above. As he buries his face in his hands, Globox arrives with the Armaguiddon, and together they chase Reflux into the starry formation: the dimension where the Leptys itself resides.
At the start of this phase, Rayman can drop down to find the game's final Green Emerald in a hidden alcove. It is not possible to reach it with a powerup active, and if Rayman falls off the tower, he must restart the entire fight from the first phase.
Final Fight - Phase 4
The final part of the final fight involves Rayman fighting on the Armaguiddon as a flying Reflux attacks with energy filaments.
The fight starts with the first-person shooting view seen in the last section of the Tower of the Leptys. Rayman must shoot down the magical shield covering Reflux's orb while also shooting down red energy filaments fired by Reflux. After doing so twice, Reflux charges at the Armaguiddon with the orb exposed; Rayman must fire a single shot to it to take off 1/3 of Reflux's health.
Reflux then plants himself into the center of the arena. With the help of Andre, he produces a large amount of Hoodlums, then creates a dark vortex beneath his body. In a third-person view, Rayman must pilot the Armaguiddon to avoid red filaments and destroy as many Hoodlums as possible using guided bombs. The Hoodlums constantly march towards Reflux, and any who get close enough without being shot down by Rayman is sucked into the vortex, restoring some of Reflux's health. After all Hoodlums are off-screen, Reflux re-sprouts his wings and restarts the first part of the fight.
The fight is always four parts, regardless of how many Hoodlums are destroyed by Rayman. The music changes with every shooting section. Reflux creates more filaments and fewer Hoodlums during the fight.
Final Fight - The End
After Rayman completely defeats Reflux, his body crystallizes and shatters, killing him and releasing a helpless André. The Black Lum Lord flees from Rayman, pleading loudly for mercy, even calling out to Globox for help. However, Rayman simply Grimaces at him, causing André to laugh and revert to a Red Lum.
- Ironically, despite being the strongest Knaaren, he is the only one you can defeat, as all the other Knaaren are invincible to your attacks. It is possible he gave up his immortality or whatever magical defenses the others of his kind have in exchange for offensive power.
- He is one of the few characters Rayman has beaten to canonically die, and the only one who has currently stayed dead.
- Reflux has an upside down arc on his forehead because he wants to retain his anger forever.