Mega Man and Rush (Mega Man Classic) fused together as the Super Adaptor.
The Cross Fusion of Lan Hikari and MegaMan.EXE (Mega Man Battle Network)
Mega Man (Mega Man Star Force), the fusion of Geo Stelar and Omega-Xis.
The Atrocity (Spider-Man: Edge of Time), a gestalt entity formed from Walker Sloan, Anti-Venom, and Dr. Octopus.
The Queen Plaga (Resident Evil 4) merged with Ramon Salazar and a Verdugo.
Mega-Mix (Crash Bandicoot: The Huge Adventure), the fusion of Dr. Cortex, N. Gin, Dingodile, and Tiny Tiger.
Ventus-Vanitas (Kingdom Hearts), a gestalt entity created from the fusion of Ventus and Vanitas.
Twinrova (The Legend of Zelda), the fusion of Koume and Kotake.
Tiencha (Dragon Ball Z: Budokai 2), the fusion of Tien and Yamcha.
Gokule (Dragon Ball Z: Budokai 2), the fusion of Goku and Hercule.
Baby Janemba (Dragon Ball Heroes), the fusion of Baby and Janemba.
Ermac (Mortal Kombat) is composed of countless dead souls.
Dark Kahn (Mortal Kombat vs. DC Universe) was created by the accidental fusion of Darkseid and Shao Kahn.
Liquid Ocelot (Metal Gear Solid 4: Guns of the Patriots), the merger of Liquid Snake's mind with Revolver Ocelot's body.
Zekrom and Reshiram (Pokemon) can fuse with Kyurem to create either Black Kyurem or White Kyurem.
Bowletta (Mario & Luigi: Superstar Saga), the fusion of Bowser's body and Cackletta's spirit.
Yuga-Ganon (The Legend of Zelda: A Link Between Worlds), the fusion of Yuga and Ganon.
Hyper Mega Man (Marvel vs. Capcom) is the fusion of Mega Man, Rush, Eddie, and Beat.
Bellumbeck (The Legend of Zelda: Phantom Hourglass), the fusion of Linebeck and Bellum.
Terra-Xehanort (Kingdom Hearts), the fusion of Master Xehanort's heart with Terra's body.
Eye-Brawl (Skylanders) is the resulting fusion of a flying eyeball and a headless giant.
Super Dimentio (Super Paper Mario), the fusion of Dimentio, Luigi, and the Chaos Heart.
Boolossus (Luigi's Mansion), the merger of 15 Boos.
The Elementium Monstrosity (Warcraft) is the abominable fusion of the Ascendent Council.
The Amalgamation (Codename: Kids Next Door- Operation: V.I.D.E.O.G.A.M.E.), the fusion of Captain Stickybeard, Knightbrace, Count Spankulot, Gramma Stuffum, the Common Cold, and the Toilenator.
Oracle has become Chaos (Valkyrie Crusade) after having fused with him, essentially becoming his human vessel/form.
Aurum Pyrrhon (Kid Icarus: Uprising), the merger of Pyrrhon and the Aurum Brain.
Shiny RoboBowser (Mario & Luigi: Paper Jam), the merger of Bowser, Paper Bowser, and several of Paper Bowser's minions.
Giant Luigi (Mario & Luigi: Dream Team), the result of numerous Luiginoids merging with Dreamy Luigi.