i see videos of people moving strangely with the bird power up but i am not sure how to do it. i just spam "A" but that is not what people do in the runs.

We do what's called "Dive Bomb cancels" or DBCs for short. you start a dive bomb by pressing down + B, and then you cancel it halfway through with A. This way you get the upwards component of the dive bomb and then the height from the wing flap, and you can repeat these really fast.

What I used to do was hold down on the dpad (usually along with a direction) and then mash A and B in a specific rhythm. Sliding my thumb from A to B repeatedly tended to give me the best results.

Makes sense, thanks for the response!