That will take some playing around with to get right. There are a few options:
- make a control assigned to starting the drift, give the player full control
- make the game detect the player's intention to drift, by looking for things like the player hitting the throttle through a turn, or trail braking
- some mix of the above two - instead of having a separate control to start a drift, just look for the player to brake too hard and steer too far to one side
- give some kind of visual feedback to the player so they can know that some assistance is occurring
A little more about MKW - to start a drift the player press/releases the B button (trigger on the bottom of the wii remote). For the standard MKW controls B is jump, drift, brake, and reverse, depending on what you're doing. If you're standing still then B goes in reverse, if you're moving then it does a hop and then brakes, if you're moving and turning it does a hop and then starts to drift. So basically to drift, you start turning and then hop and hold down the button. This is when the changes I described in input filtering begin to take effect, the steering is reversed and limited or focused on a small range of directions. To give visual feedback, blue sparks start to fly out of the rear tire(s) of the kart/bike.