Bowser Jr Special Reversal Tech

[Ya Bebto]

Bowser Jr has some interesting properties on his side, down, and neutral special with respect to reversals. Each move can be input backwards (downward diagonal for down special, slight tilt on lower sensitivity for cannon) which isn't revolutionary. However, there is a second window to reverse with separate properties exactly three frames later on each move. Reversing at this point will reverse your momentum, sending you the opposite direction of wherever you were going (the car reversal just makes the windup shorter, but the hitbox comes out at the same time). These reversals are not mutually exclusive, meaning you can run and jump, input to drop the mechakoopa behind you, then reverse it a second time to actually drop it forwards, but move backwards. You can also double cancel the cannon in the same manner.
You can act on the first frame after jump cancelling out of the car, and it takes three more frames to reverse your momentum from the car. These inputs can be extremely difficult to do normally, but they are actually much easier to do jumping out of the car, as most missed inputs would normally be interpreted as a car input. This lets you charge at someone in car, then fly away charging the cannon in just 4 frames.
I found this recently in training so I haven't had a ton of time to experiment, but the inputs are doable with practice. I can already do them out of car decently well and I'm terrible at most precise inputs. It also explains why trying to drop mechakoopa backwards seemed to be so finicky.

 

[Ya Bebto]

After some testing on the ledge, you can jump and double reverse a cannon shot to start charging it immediately while staying over the ledge, letting you shoot it at stage height and still grab the ledge afterwards, whereas you'd normally land on the stage for its backswing unless you released it way above the stage. You can do the same for mechakoopa, but the backswing is much longer and you won't grab the ledge.

 

[Glicnak]

Dude this stuff is insane. I think the biggest application of this will be cart fake-outs (easily makes jump/drop mech waaaaayyy safer).
But I also think this is going to be an automatic combo-ender. We don't really have many combos or even long strings because of the knockback and angle of most of our moves... Using this double reversal at the end of a combo will give us better stage presence after hitting them away and place the mecha koopa closer to the middle of the stage too. I'm not home to test it but this could potentially mean we don't need to choose between setting up and catching their landing. We might be able to do both fairly consistently with this.

 

[There Goes Bill]

Hey i just found this out myself and i found this post, try double tapping the b button while rolling the stick down forward or backward. i don't really understand the concept behind the cannon ball one am, i can spin around with it the first time but i dont use lower sensitivity so im guessing this wont work for me.

Awesome post cant wait to see this used

 

[VodkaHaze]

It seems as if the cannon techniques are called B-reverse and wavebounce. They've existed since Smash 4. Did not know you could do that with Mechakoopa though.