Fusion-Matter is the "green goo" that Lord Fuse is using to infect the Cartoon Network Universe and is basically the main strategy in his conquest: by sending Terrafusers down to a planet, Fuse begins to spread Fusion Matter across it, slowly infecting the whole world. Once a planet has been infected to a certain point, Planet Fusion can just absorb it.
Fusion Matter itself is collected throughout the game. All the Fusion-Monsters and Fusions that are found in the game are made of Fusion Matter and defeating them releases a certain amount of Fusion Matter that will be collected. Doing missions and Infected-Zone races also gets players Fusion Matter. Fusion Matter itself can be used for various purposes: If players collect enough Fusion Matter, they can make a Nano by defeating a Fusion, and can also use it to change the Nano's power.
Other characters in the game have also shown that it can be used in machinery and to create genetic experiments.
Fusion Matter in its raw form is very toxic and harmful to its surroundings. Living creatures such as the player can take damage if they come into physical contact with Fusion Matter; prolonged contact with it is lethal. It has also been known to mutate many different creatures and objects into horrible Fusion Monsters, if they are exposed to it in a non-lethal way.
Fusion Matter is also known to break down the environment itself: the living floor in an area usually ends up dying, or mutating into unrecognizable forms, and the ground itself can crumble apart. Inside Infected Zones, the infection of Fusion Matter can even distort gravity, creating floating platforms and floating debris.
Fusion Matter can be molded and used to create various monstrous lifeforms such as Fusions and Fusion Monsters. These lifeforms can also be combined with the environment and other materials to form bigger and more varied creatures. Creatures that are composed of or influenced by Fusion Matter are usually being controlled by Fuse. For example, when Kevin 11 tried to absorb Fusion Matter to use it against Fuse, he ended up being controlled by Fuse instead.
Fusion Matter is known to appear in three forms: a liquid form that creates infected patches and lakes throughout the game, Fusion Matter in its raw form, and a green gas that can be seen in the air, but is harmless.
After players rid the Crystalline Caverns of their Gooby Trap in "Mystery of the Meteor (Part 5 of 6)," Gwen Tennyon tells players that Fusion Matter is not only used to infect the planet, but also for Fuse to communicate with his minions. This could possibly mean that Fuse does not have to be on Earth to attack it.