A technique that I've been secretly working on, but kind of gave up on using it competition is a quicker, lower to the ground z-air. I was trying to find a way to cover a far distance at ground level with a melee attack for characters like Metaknight, Sonic, and Squirtle. I first tried doing short hop, airdodge, zair, but Link falls too quickly and the zair doesn't cover that area I want. What I figured out though is that if you slightly airdodge upwards before you zair, the momentum from your airdodge will counter act your natural falling momentum and Link will float in place while doing the entire zair.
So to do the technique, you jump and quickly airdodge while barely, just BARELY tilting the joystick up, then pressing z. If done right. Link will float at near ground level and fire his z-air. It's not too hard to do in training, but the difficulty comes in getting your muscle memory to barely tilt during a fight. I think once mastered, it will be an incredibly effective poke against short characters.