Honestly most reflectors are a commitment. I think a big part is that if you're trying to throw projectiles from across the stage, then it is safe for them to reflect them without any chance of being punished. You should try to stay in a mid-range where you can still throw projectiles safely, but you're always threatening approaching. YLinks worst match-ups would be fox+wolf+falco, lucina+shulk+roy+chrom and pika+pichu. I believe that all these match-ups have plenty of counter-play and I believe that YLink is solo main viable.
Out of the characters that have reflectors, the toughest ones would be fox and wolf. I'm still trying to get better at those matchups so I don't think I can give much advice. If you're struggling against palu or mewtwo or those sorts of characters, focus on how YLink outspeeds them and how well he combos them.
Bouncing your boomerang as well as throwing bombs can be good against reflectors because you can throw them in a way where they won't hit you on the way back.
