I came up with a double-jump cancel technique called
"Telekenetic Drifting" (it may already exist though), and how it's done is you jump in one direction, then when you are ready, you double jump in the opposite direction of where you jumped in and attack in any direction with the C-Stick.
for example: Frame 1:
+
or
Frame 2 - Frame 30
ontinue holding
Frame 31:
+
or
Frame 32-(whenever the stall of the double jump ends)
ontinue holding
+ tap
--
The result is that Mewtwo would jump forward, then use the technique, making Mewtwo fly backwards with his fair at about the same speed as a forward dash-jump.
Whats happening?
when you do a double jump as Mewtwo, Ness, Yoshi, or Peach, due to their double jump having the status as "delayed" double jumps, if you attack before a certain point, you cancel the scheduled rise. You guys know that, that's how Ness can combo in Smash 64,
but, what they didn't tell you, is that the ultimate horizontal momentum gained from the double jump is always present, and since all double jumps defy physics and shift your direction to the one you double jumped in leaving no trace of which direction you jumped in prior, you can manipulate this by jumping in one direction, double jumping in the opposite direction which defies your first jump, then attacking with the C-Stick.
This can work as a way of safely using a Shadow Claw as Mewtwo without the risk of getting hit, mindgames, since you are essentially "fading in and fading out" like Wario, Combos, since with proper timing Ness can combo with his bair by doing this, Extra Special Momentum, since Ness can use this to boost the horizontal momentum of his PK Fire or temporarily "glide" with his PK Thunder.
You actually don't need to jump in a direction to do this technique, however, if you don't, then you take away the mindgame aspect, though, you still need to jump.
If done correctly, your vertical momentum will still get cancelled, but if done at the latest possible time before the technique fails, your character will pop up a little bit while using the technique, any further rise means you did the technique incorrectly