Aether is, essentially, not an option in this fight. If Mario has good aim he can send his water stream to catch you at the ledge even at the lowest height. Best of all is to simply get back without needing to use a recovery move at all, but that's not always an option. Your most reliable recovery move is going to be using Quick Draw while still high up, to sail right over Mario's head so he can't cape or Fair you without telegraphing it with a full jump and double jump, in which case that's your cue to keep holding Quick Draw and go for the ledge (or if you're high enough and charged enough, to release it because Mario's air speed isn't fast enough to go up that quick). If he starts anticipating this and runs back to catch you with an Usmash, that's also when you go for the ledge, although depending on the timing you'll likely still go too far and too fast for him to catch you.
Most of Mario's attacks will send you high up, so this isn't very hard to do. However, Mario's Dsmash and Fthrow will send you at a low angle, so avoid fighting with your back to the edge as much as possible, even when you're not approaching death percentage.
