How to perform it.
1. Spin Dash (side b)
2. Immediately press shield button/jump button.
3a. If you press shield you can shield grab making your opponent think you will spin dash to them, tricking them.
3b. Or you can press jump button right after spindash attack to perform a mind gameable spindash that goes up in the air instead of straight to your opponent, follow up with aerials next. (less info)