Link is widely considered to be on the lower end of the cast. His difficulty with fast characters and their relevance in the meta are strong reasons why. Don't let this discourage you. There is much counterplay to fast characters and if they are not careful, they will realize just how quick one mistake will cost them 60% as Links early % punish game is simple and effective on most of the cast.
Do not use Zair against fast characters often. ****ty hit bubbles and 15 frames of landing lag are not worth the risk, when there are better options. Nair is a great option. Not just as an oos option. Along with proper DI during combos you should be mashing nair to interrupt poorly timed strings by your opponent.
Keep as many of your projectiles out as possible while you are in mid range and try to approach with a bomb in hand and a boomerang in the air. Holding stage position near the center is paramount for Link, don't let them believe they can bully you around the stage. Link very poor recovery distance when below the ledge will have you losing stocks at 50% against characters with low angled moves.
The best way to deal with fast safe shield pressure for link is to buffer roll OOS, or use Links top tier spot dodge into your fastest options which I will go into later.
Nair oos when you find an opening. Up-B when someone makes a big mistake. Do not try and shield grab most fast characters, as Link cannot grab other characters out of the air for much of his grab distance, and his tether grab is 11 frames to come out.
Links friction was reduced in 3.6 so Wave dashin, wavelanding and perfect wavelanding can help with micro spacing. Follow this with your fastest moves if you see an opening. This would be any 7 frame move. Jab would be safest, but is very CCable (mind your spacing). Followed by Dsmash, then Dash attack. Those 3 moves are your fastest at 7 frames a piece. Keep in mind 7 frames is quite slow. You must be very tight with your timings as nearly every character in the game will out speed you if you aren't. Including Bowser and DK, who have faster options than you by a wide margin.
Having a bomb in hand allows you to Bomb OOS. Just make sure you are at a good distance. Hitting both you and your opponent with the bomb explosion will almost always lead you to being punished for it, due to Links sluggishness and combo weight.
One more thing to note about Link. Get very used to trading, and converting off of trades. My years of playing Link have show that to be one of the strengths every link main should get accustomed to. Those fast characters will win neutral and try to run a train on your poor defensive options, and lack of speed. Often a stray boomerang, Z dropped bomb, quick nair, and fast teching reflexes will mean the differences between winning and losing for Link. Counter hits and the ability to react to them are a must as a Link player. You do not have the defense or offense to afford a missed opportunity.
Crouch canceling is a great mixup and has few negatives for link. You will be able to counter hit them for hitting you and get a conversion started with a 7 frame Dsmash (DO NOT USE DTILT THIS MOVE IS GARBAGE. They have to do something really dumb for this to work.) or get the all important stock with a quick CC 8 frame up-b. Links fastest killing option. Keep in mind that if you hit anything with Link's up-b, in the air or on the ground, you will lose your ability to blow up a bomb for bomb jumping for the next 9 moves you hit with. I've found that up-b's usefulness in killings is more important than saving it for your bomb jump, as he has a lot of trouble taking stocks without this or his bad grab, amazing dthrow kill setup.
THINGS NOT TO DO WITH LINK IN NEUTRAL:
Do not Ftilt. This is the slowest ftilt in the entire game at frame 17 (when the move is in front of link) with very punishable endlag. Don't let it's range fool you. Hope that you accidentally get an fsmash when you try in vein to make Ftilt hit anything. Fsmash is faster, safer, kills better, has huge range, and mixup potential.
Do not Dtilt. This move is slow as well at frame 10, (frame 11 at a usable range) The angle and speed of this move make it nearly useless. You are better off always using dmash, which outclasses dtilt in nearly every aspect. Prepare to get punished when you try to dtilt someone.
Do not pretend Jab Jab > anything is possible or safe. This is a great tool for link, but it is very easily CC'ed, shield grabbed when not spaced properly, or just Sdi'ed out of. Use It as a mix up.
Do not thing that nair will protect you from everything for free. While this move is the cornerstone of links toolkit. You must remember that it is not always a safe option, or bigger than your opponents own large hitbubbled moves.
Do not always come down with Dair. While this is a great mixup and move, it is quite slow, and very committal. AGT Bombs and nair are usually better options. If you are fighting a character that outclasses your ability to get back to stage from the air, consider keeping a bomb in hand and timing a Z drop to cancel your momentum from their attack. This is a very good counter and will allow you to get back to the stage more often than not.
Do not always Tech. Links get up attack is very useful, and even good players will fall prey to this option. In contrast, Link is very easy to tech chase, and keep in a bad position. Mix that **** up.
Do not throw boomerang when close to an opponent. This is not melee. Your boomerang no longer does 17% up close. Meaning it will almost always lose to they attack your opponent is throwing out to hit you. Their attack must only be 5% more than your 11% boomerang to ignore it outright and **** you up.
There are more, but these are important.
This all assumes good play on your opponent. If you use even half of what I have typed up here on a mid level player, prepare for the Link ditto and cries of how easy link is to play and how up-b is too gud. People that can't deal with projectiles or being hit for getting hits will quickly become frustrated with links large lingering hitbubbles in my experience.
