Like Nanos, Fusions are created by means of special items that are dear to the character they are based on being combined with Fusion Matter. For example, the first Fusion ever created, Fusion Samurai Jack, was formed using a sandal stolen from Jack by Fusion Spawns. Reports say that certain Fusions have been created within The Darklands.
Fusions reside within Fusion Lairs, which are normally large caverns with a maze-like structure and Fusion growths within them; these Lairs have Fusion Monsters along the path with the Fusion itself residing at the end of the path. However, some Fusion Lairs, such as Fusion DeeDee's Lair, are large and open, with futuristic walls and spread apart enemies and the Fusion itself having its own separate platform or area in which it resides. Fusion Lairs are entered via Fusion Portals, which are green warp pads with Fusion Matter tentacles protruding out of them. Unlike Infected Zone warp pads, however, you can only enter a Fusion Lair during the specific mission that has you enter it.
Sometimes an NPC will be inside to pick up items players have found, give them information, or even fight alongside them. They will be a part of a player's group and will walk blindly in a set path, attacking any monster in their way or nearby. This only occurs with Eduardo, Billy, Professor Utonium, and Grim.
It is possible for a Fusion to give out a different Nano than their NPC counterpart:
- Fusion Tetrax creates Humongousaur
- Fusion Demongo creates Aku
- Fusion Hominid creates Titan
- Albedo creates Rath, being the only NPC fought to create a Nano.
There can also be multiple copies of certain Fusions, and it is possible for copies of the same Fusion to give different Nanos:
- Fusion Bubbles creates her own Nano and the Johnny Bravo Nano
- Fusion Finn gives out the Jake Nano as well as his own
The only time you don't have to fight a Fusion to create a Nano is during Unstable Nano (mission), where Dexter, who by using certain things that you collect for him, creates the Unstable Nano via the Nano Creation Machine.
List of Fusions
Lairs containing other enemies
|Enemy||Lair||Location||Infected Zone||Mission||In Retro|
|Kevin||Foster's Home||Foster's Home||None||Kevin Help Us (Part 3 of 3)||Yes|
|Albedo||Albedo's Lair||Mojo's Volcano||None||Let Me Tell You About Rath!|
|Vilgax||Fusion Juniper's Secret Lair||Upper Catacombs||None||Avoid the Planetoid (Part 4 of 4)||Yes|
|Vilgax, Mojo Jojo and Mandark||Ammunition Depot||Offworld Plaza||Skypad Space Port||Yes|
|Cheese Fusions||Foster's Interior||Foster's Home||None||Sorted Cheeses|
|Hootie||Blowfish Lair||Peach Creek Estates or Peach Creek Estates (The Future)||None||A Thanksgiving Delicacy (Part 2 of 2)|
|Fusion Mega Echo Echo||None||Genius Grove||None||None|
|Fusion Mini Echo Echo||None||Genius Grove||None||None|
|Bad Max||None||Peach Creek Estates||None||None||Yes|
|Lord Fuse||Fuse's Throne||Fuse's Lair||None||Fuse No More (Part 4 of 4)||Yes|
In addition to altered names, some Fusions also have distinctive mutations:
- Fusion Professor Utonium has tentacles protruding from his back, which look like the equippable Nergal Tentacles item.
- Fusion Numbuh Five has two Pop Gun pistols.
- Fusion Numbuh Two uses a F.L.A.P.P.U.H to fly or hover above the ground, whether he is attacking the player or not.
- Fusion Princess flies on her jetpack.
- Fusion Numbuh Two has a mirrored "2" on his flight helmet.
- Fusion Flapjack carries a big anchor.
- Fusion Professor Utonium used to be known as Professor Plutonium.
- Fusion Ace does not wear sunglasses, while the real Ace does.
- Fusion Numbuh One is wearing a gas mask and has a trio of gas-masked Fusion Spawns over his head.
- Fusion Numbuh Three has claws coming out from her sweatshirt's sleeves.
- Fusion Fuzzy and Fusion Billy can distinctively climb walls.
- Fusion Mayor's monocle appears to be a bionic eye of some sort, but that may just be due to the Fusion palette.
- Fusion Mojo Jojo uses a raygun-like pistol.
- Fusion Wilt has a number of cybernetic implants on his body, which inspired by the real Wilt's alter-ego Lord Snotzax Super Meany-Beany Baron von McNasty.
- Fusion Bloo and Fusion Cheese have jagged mouths.
- Fusion Dee Dee is missing stockings completely.
- Fusion Bubbles's Octi backpack is sporting an evil face.
- Fusion Mr. Herriman has the monocle on the opposite eye.
- Fusion Gunter, Fusion Numbuh Four, Fusion Bloo, and Fusion Scotsman are bigger than other Fusions.
- Fusion Lee Kanker is very small.
- Fusion Tetrax is riding a hoverboard.
- Fusion Frankie has Mojo Jojo's symbol on the shirt, while the real Frankie has the Powerpuff Girls' symbol.
- Fusion Rex has a tiny smackhand instead of a regular hand, suggesting it is part of Fusion Rex's normal state.
- Fusion Vilgax, Fusion Kevin, and Fusion Gwen are in their old forms.
- Fusion C.L.Y.D.E.'s have broken panels and an angry face.
- Fusion Frankie and Fusion Courage jump at a great height when they're attacked.
- Fusion Max uses a rifle similar to the rifle an SACT agent uses.
- Fusion Computress has gun barrels with spiked foresights as limbs instead of regular hands.
- Fusion Gunter has a brain coming out of his head.
- Samurai Jack has more than once claimed that Fusion Jack is the first Fusion to have been created after his sandal was stolen; he followed the statement by saying that facing him means certain doom.
- After the Thanksgiving 2009 event, Fusion Blowfishes (Rudy, Cootie, Tootie, and Judy) have been placed randomly around the FusionFall universe. However, Hootie cannot be found since it was in the Future, which no longer exists.
- Not all Fusions are named after their counterpart. Most are simply named "Fusion (character name)," but Professor Utonium's Fusion counterpart is dubbed Professor Plutonium.
- During development stages of the game, it was possibly intended for Fusions to roam freely outside of Fusion Lairs instead of exclusively appearing in Fusion Lairs (as seen in one of the original trailers for FusionFall), although they did implement this with Fusion Mega Echo Echo.
- Fusion Finn and Chowder are the only new fusions fought twice.
- Fusion Courage, Fusion Prof. Utonium, and Fusion Scotsman are the only Fusions that appear in the same infected zone, but in different lairs.
- Fusion Buttercup appears in the same area, but her lair is outside, while her Secret Lair is inside the infected zone.
- Fusion Ben had two lairs in the same area, but after the expansion of February 16th, 2011, he now has three lairs, the last being in the Null Void, which is technically a Containment Unit.
- Out of everyone players fight in a lair, only Mandark, Mojo, Vilgax, Kevin, Mandroids, and Albedo are actual NPCs.
- If players use a Stealth Nano and linger around Albedo, he will make the same comments that he used during the Birthday Bash.
- The Fusion Buttercup fought in the "A Personal Matter" Nano mission is sometimes if not always glitched. These glitches affect her gameplay and attack patterns. Some of her most notable glitches are that she and her minions remain frozen for long periods of time during a fight and that she is unable to recharge her health if the player retreats.
- Prof. Plutonium's tentacles make him somewhat reminiscent of the Marvel Comics character Doctor Octopus.
- Fusion Numbuh Three's claws are likely a nod to the Jiāng Shī girl, Hsien-Ko, from the Darkstalkers series of games. Both Kuki and Hsien-Ko are Asian in nationality and wear oversized sleeves.
- Hootie, Rudy, Cootie, Judy, and Tootie have no non-Fusion counterpart, but are based on the blowfish from an episode of The Powerpuff Girls.
- Hootie might be a nod to the band Hootie & the Blowfish.
- Some fusions have inconsistent eye colors between official sources. For example, Fusion Mandark's eyes are yellow on the loading screen, but in the game they are red.
- Fusion Wilt has the number 0 on his chest while the real Wilt has the number 1 on his chest.
- Fusion Bubbles, Fusion Ben, Fusion Edd, and Fusion Eddy are the only fusions to be fought three times in the game.
- Unlike other Fusions, where the Fusion itself is found at the end of the lair, Fusion Mayor's Secret Lair has the Fusion in a cavern right next to the entrance, though defeating him doesn't count for the relevant mission until players defeat the monsters in the caverns in front of players.
- Fusion Amphibian, Fusion Spidermonkey and Fusion Echo Echo (as well as Fusion Mega Echo Echo and Fusion Mini Echo Echo) are the only fusions to be one of Ben's aliens.
- Even though their NPCs were updated, Fusion Gwen, Fusion Kevin, and Fusion Vilgax still have their old design.
- Fusion Hominid is internally referred to as Hibagon, a cryptid from the Secret Saturdays. It was originally meant to appear in the Monster Island expansion as a normal Fusion monster, but was repurposed for the Titan Nano mission.
- Fusion Eddy 's lair was originally in Mandark's House in Genius Grove , where Fusion DeeDee 's lair is in the past. He was later moved to Pokey Oaks Junior High where Fusion Blossom 's lair is in the past. However, his base still styled for Mandark's House , not Pokey Oaks Junior High .
- Although most Fusion Lairs have only one type of regular monsters within them, there are various exceptions:
- Fusion Frankie's lair, which has Extremospawns and Scribble Spawns
- Fusion Chowder's lair, which has Ball-Peen Meanies and Pesky Ponies
- Fusion Hominid's lair, which has Motorillas and Silverback Motorillas
- Fusion Fuzzy's lair, which has Turbo Ventilators and Weird Welders
- Fusion Numbuh Five's lair, which has Scribble Spawn and a Crazy Scribble Spawn
- Fusion Blossom's lair, which has Maelstrom Creepers and their bosses, Maelstrom Brutes
- Fusion Cheese's lair, which has Shellslugs, a Meteoric Sentry Number One, and Eyebulbs.
- Fusion Coop has Cephalopod Alphas in his secret lair
- Fusion Him's lair has Dumb Jock-O-Lanterns
- Fusion Juniper Lee has Bloated Cryptworms in her lair
- Fusion Mojo Jojo's lair has Flashing Razor Mantises
- Fusion Utonium has Turbo Ventilators
- Fusion Edd has Elder Skeeter Spawns
- Fusion Ben has Clawbreaker Furies
- The Fusion Kankers have Giga Shellworms in their Fusion Control Center
- Fusion Ed, Edd n Eddy have Great Shellslug Kings in their lair
- Fusion models in-game are larger and taller than their normal counterpart's models.
- However, Fusion Bloo is naturally larger than the normal Bloo.
- Fusion Gunter is the only Fusion to receive a redesign. His new design bares a resemblance to his true form, Orgalorg.
- Fusion Dracula has the noises of Fusion Jack.
- Fusion Ice King also has the noises of Fusion Mayor.