killing fox is not as hard as u might think
for ylink vs fox, the main focus is getting a knockdown. ylink has several very fast moves to do that, such as dash attack, nair, uair underneath his jump, sh fair, or whatever. however, the best option is to bomb. after ylink gets the knockdown, you just have to capitalize on fox's wakeup options as much as possible. this is where ylink's grabs can get pretty good, however there aren't really any good grab combos aside from dthrow tech chasing. if ylink can't capitalize on the knockdown, he can choose to pull out another bomb. as long as the percent is high enough that a bomb will knock down, ylink can fight fox.
once fox is around 70~80ish, ylink can score quick hits such as nair or dash attack, or uthrow followups (not necessarily true combos) that will knock fox of the stage so that ylink can edgeguard. the matchup is possible, and i think it's about on par with link's. it just takes a lot more patience and tech skill.
just wanted to give a picture of the matchup. a nair against fox at around 110 usually puts him at a realllly bad position to get edgeguarded. unless it's dreamland or something, but that stage is good for the kid too.