So after talking with @ Bizzarro Flame about how to use upair to cover spacies side-b and up-b sweetspot attempt, and saying that youfast fall it, I now have concrete evidence to show why you shouldn't FF the upair if you want to hit it at its lowest possible trajectory, and that it can also cover the edge of the side platform all the way to below the ledge.As you can see here, getting the 16th frame of upair is crucial, as it is the lowest hitbox that can be output from upair. This image above is one of the lowest, if not the lowest possible 16th frame of the move to reach below the ledge. You can even move a bit to the left or right so that you don't risk your hurtbox being hit, so the leniency there in terms of horizontal positioning is rather fair. You'll rarely overshoot or undershoot as long as your foot,is almost touching the ledge.Now why to not FF instead of FF: If you jump, and wait until frame 16, 17, or 18, (roughly just as you are starting to fall from reaching the apex of your jump; react to you reaching the apex of your jump to time this right) you will get the 16th frame of upair to land below the ledge, and frame 18 is the perfect frame, as it's what happens in the image above. If you upair on frame 19 of your short hop, you'll only get frame 15, which doesn't go as low. If you upair on frame 15 of your SH, it will still go pretty low, but not exactly below the edge.If you DO fast fall: You have to start upairing on frame 9 or 10 of your jump, and then start fast falling on frame 7 of your upair, you will get frame 16, but it won't be as low. In fact, if you're even slightly off with the FF timing, you'll end up getting the horrid frame 15 that isn't good a lot more often than you would if you didn't fast fall.So all in all, not fast falling gives you a 3 frame leniency at LEAST to get frame 16 and go below the ledge.If you Fast Fall, you're at a much higher risk of falling too quickly and getting frame 15 instead of frame 16.For a visual cue on when to upair (since you won't need to time the FF because you're not doing it) on Battlefield, just look to upairso that at the beginning of the upair, your leg alligns with the side platform on BF.For Yoshi's Story, it's the same relative thing as BF, but the really cool thing is the beginning of your upair can cover all the way to the end of the platform on YS, so you can wait until Fox up-bs at a high angle and hit him on the way down, even if he's about to land on the platform, even just staying in the same position you'll still hit him haha. Yoshi's too good.For Dreamland, it's just a bit below the platform.For Pokemon Stadium, it's also just slightly below the platform, but not as much as on Dreamland.For FoD and FD, you'll just have to just the apex of your jump as a visual cue.