How to cancel King DeDeDe’s Up Special

There are a few major new/changed mechanics that we currently know of:

• Random tripping has been removed; forced tripping is still in.
• You cannot grab a character if you've thrown them in the last second (no chaingrabs).
• There is no longer a difference in edge actions upon reaching 100% damage.
• Edgehogging has been removed; instead, the incoming character will steal the edge from the current occupant.
• It appears that swimming has been removed; characters will just fall through water as in Melee.
• Directional influence has been revamped. In previous games, you could change the angle of your knockback by holding perpendicular to it. In SSB4, you instead add a vector in your holding direction, which can alter both your angle and your distance.
• Characters at high damage deal slightly more knockback.

There's nothing more to unlock via the stage builder. With any luck, Nintendo will add content in subsequent updates.