Arsenal roulant in french, might be "Rolling Armory" in english for 20Gs.
Use each weapon in the game at least once.
( Weapons in the DLC doesn't count)
There's 14 power ups you can find in a game,
Mine, Missile, Drum, Supersonic Bang, Flamethrower, Electric Blast, Drone
Mortar, Gatling, Flash, Shotgun, Electrochoc, Plasma Gun and the Wreckball
You can find every one of them in the level Ice Bridge ( and others).
You can set a custom game in local multiplayer with 2 controllers, and when they ask you to choose the weapons for the race, select "Chaos" and choose "All". Search for every weapon on that race. Or simply play online multiplayer and concentrate on finding all the weapons.
Edit : As stated by JJBDude48, if you're having trouble getting your last weapon, you can stay on top of a Bonus, and press Y right away to delete it from your inventory and collect a new one until you have your weapon of choice.