Walkoff fair. Walkoff fair. Walkoff fair. Walkoff fair.
Master the timing, the spacing (this isn't hard), how much you can fast-fall without dying (this actually is kind of hard because ledge sweetspot sizes were reduced and it's harder to Aether back after dropping too fast, be careful.)'
Also learn to space a down-tilted FTilt at the edge, especially after a wavedash. Absolutely bones Side-B recovery.
If a spacie is Up-B'ing below the ledge though and you don't kill it, (read: You didn't WALKOFF FAIR) then you are BAD and you should FEEL BAD for throwing away your chance at victory. QD -> Fair can even get you quickly out there when they're level with the stage and in Up-B startup, so you can hit them out of it before they even move, thus eliminating the need for guessing.
Basically Fair is awesome and if a spacie Up-B's anywhere offstage, it should be dead.