Donkey Kong's Hand Slap has always been one of his riskier options. While good at racking up damage and catching rolls, its long animation leaves DK open to punishes - both on whiff and on shield. With all of this in mind, Beefy Smash Doods have released a video covering a newly-discovered technique that can make this move safer and more versatile.
Discovered by KDK and further refined by himself, Proctavia and Will "DKWill" Walsh, the new technique allows Donkey Kong to instantly cancel the move's animation by performing a Hand Slap right as he auto-cancels an aerial upon landing. On most platforms, this will interrupt the move before the first frame with an active hitbox. This is useful for baiting opponent into shielding or trying to respond with an unsafe option, but has little utility outside of this.
The Slap Cancel really shines on rising and sloped platforms. With the correct timing and positioning, Donkey Kong's Hand Slap won't be interrupted until after the first hitbox comes out, changing the move from a slow, high-risk high-reward punish tool to a quick combo starter or extender. This version of the technique works on both Town & City and Lylat Cruise, though it has far more utility on the latter. Beefy Smash Doods' video explains just how it works and shows off a few potential applications, and KDK has a few examples of his own on twitter.