Jigglypuff
Preface
This will cover techniques important to Jigglypuff.
Pivot Landing
Whilst a universal mechanic, Jigglypuff gets the most mileage of this technique. Pivot Landing allows a long slide across the floor, deeply buffing her grounded movement as a very important mixup. This is performed by holding the opposite direction when landing. This can only be done out of an autocancel or empty jump. As Jigglypuff's aerials essentially all autocancel, she can use pivot landing as a very effective movement mixup out of it, even making certain approaches not committal.
Down Air Pivot Land Up Tilt
An extension of the pivot landing technique. It's highly recommended to use tilt stick for ease of this technique. Out of a rising down air, without a fastfall, hold back when landing, and simultaneously hold up on the C-Stick. Ensure when doing the down air, you are slightly shifting forward - in order for the opponent to get launched behind you.
This allows many more combo extensions for Jigglypuff. Typically IDJ Down Air, IDJ Up Air or Rest.
Sing Tech Trap
Doing Sing 2-15 frames before a tech, covers all tech options on a battlefield sized platform. (Credit to @drakeirving on Twitter for labbing this). This is useful after doing a down air pivot land up tilt underneath a platform, up air and pound. This can deeply enhance her punish game on stages with platforms.