The C button can refer to buttons on the Nintendo 64 controller or a button on the back of the Wii's Nunchuk auxiliary controller.
Nintendo 64 controller
The C buttons are four small, yellow buttons found on the top right area of a Nintendo 64 controller. All four buttons are used for jumping, and are used to change colors on the character selection screen.
GameCube controller
The Nintendo GameCube controller's equivalent of the N64's C buttons is the C-Stick, which is used by default in Super Smash Bros. Melee to activate uncharged smash attacks.
Nunchuk (Wii)
The Nunchuk controller has a C button on its back, which is by default used in Super Smash Bros. Brawl to jump in the Wii remote + Nunchuk control scheme.
| Controllers and buttons | |
|---|---|
| Nintendo 64 controller |         
|
| GameCube controller |           
|
| Wii Remote (and Nunchuk) |           
|
| Classic Controller | L R        
|
| Nintendo 3DS |            
|
| Wii U GamePad / Pro Controller | L R            
|
| Joy-Con |                
|
| Switch Pro Controller | L R 
|
| Third-party controllers | Hori Mini Pad · Arcade controller · Keyboard |
| Other | Smash Controller · Controller modification |