Archived KimimaruSmash video from YouTube. Original description mostly intact:

Both Mario and Luigi have an extended recovery that gives them the maximum height possible. This is known tech, but I thought I'd share my method of doing it.

Frame data on the extended recovery here: http://smashboards.com/threads/mario-...

My method consists of doing it all as one swift motion for maximum consistency. Steps:

1. Input Up and Away (diagonal) on the control stick and press B at the same time. On your N64 controller, it's easiest to get the Up and Away input by putting the control stick on the notches closest to the top that aren't at an X value of 0 (so upper right notch when facing left and the upper left notch when facing right)
2. Let go of the control stick to reset it to neutral

I find it easiest to do this in one swift motion by flicking the control stick and pressing B. If you're turning around, you're holding Up and Away too long.

If you're having trouble, it helps to look down at your inputs while you do them. For further help, I recommend using 1/4 or 1/2 speed in Training Mode and letting go of the control stick once you see Mario/Luigi start the Super Jump Punch (Up + B) animation. Hyrule Castle is the best stage to practice this on since you'll land on the second platform from the ground only if you perform it; no other Up + B angle will give you enough height to land on it.

This has more applications than it may seem. It gives you another recovery option and allows you to fall a little longer to get more horizontal distance, as Mario/Luigi move very slow horizontally in free fall. It's also useful if you need to wait just a bit longer for a ledgehogging opponent's invincibility to run out and a normal recovery wouldn't. Furthermore, flicking the stick allows you to DI however you want after you perform the Extended Up + B.