1. go on a stage that has a recovering hole in it(Bridge of Eldin works Best)
2. Get a smash ball
3. Wait till that guy bombs the bridge
4. when the bridge is getting restored, use the final smash
5. if timed correctly, Jillgglypuff will be blasted up, then fall back down
6. voila, permanent puff up
7. to cancel, die, or use the final smash again

if yoshi, or kirby/yoshi swallows you, you will come out twice as big