Step 1: Pick Kirby
Step 2: Get into the game
Then after that you can either
A. wait for the AI to go full retard and azen dash straight off the stage.
B(Kirby needed). Hold A right next to the CPU just far enough so that the attack doesn't actually hit. The CPU will literally just sit there with its shield up until it breaks. Then just smash attack them off stage.
I just found this out today.