NES games not compatible
Bandit Kings of Ancient China, Castlevania III: Dracula's Curse, Cheetahmen II, Challenge of the Dragon, Crystal Mines, Gauntlet, Gemfire, Jordan vs Bird: One on One, Laser Invasion, La Empereur, Mad Max, Nobunaga's Ambition II, Paperboy, Pipe Dream, Rad Racer II, Romance of the Three Kingdoms II, The Krion Conquest, Uncharted Waters, WWF King of the Ring, WWF WrestleMania Challenge
SNES games and accessories not compatible
The Incredible Crash Dummies, BatterUP, E.V.O.: Search for Eden, Street Fighter Alpha, Star Ocean, Kirby Super Star, Super Mario RPG: Legend of the Seven Stars, Super Bomberman 2, Super Scope 6 Gun will work but you can not use a controller it wont let two player mode work on Terminator: Arcade, Metal Combat, etc.
At times different copies of the same game can work differently in
the FC Twin. This may be explained by a malfunction with the cartridge
itself. Some copies of Dragon Warrior or Super Mario Bros. 2 for example
will not work in the FC Twin; while other copies of the same games will
operate in the same machine. In other cases, the system simply does not
function with certain expansion chips, such as those in Castlevania
III: Dracula's Curse.
The FC Twin has Super Nintendo Controller Ports and you can use original SNES accessories, and you can not use NES accessories that means you must purchase the FC Zapper gun.