I think you need to jump more in general. You stay very grounded, rarely jumping and never short hopping. Nair has great priority and the hitbox stays out very long, so it's effective against a Jigglypuff approaching through the air (I think you'll trade hits with pound).
Using grabs sparingly is a necessity as Link, as his grab is very punishable. What you can do, however, is chase a back roll. You played a very predictable roller in Jigglypuff; those sorts of people tend to roll away after they've used a punishable move. Just chase them with a grab -- our range is huge, so the spacing is easy.
Well, you used it 5 times in the first match, and it only hit the last time. It earned you the final kill, sure; but you also got punished for using it numerous times. It
can be useful out of shield: it's great for punishing ledge get-up attacks, as it launches the opponent at a great trajectory setting them up for gimping.
A few additional remarks:
- If the first hit of Fsmash lands on shield, don't use the second one: it is extremely punishable.
- You only use grounded arrows: don't forget you can jump and shoot an arrow too -- you can control the trajectory with it.
- You tend to jump into people after you've been launched, generally with a Dair -- that is very dangerous, as they can hit you with a smash attack or shield it and punish: consider simply jumping away and drawing a bomb when they're waiting for you to jump back.
- When you are on the ledge and have a bomb in your hand that is about to explode, using a get-up attack/normal getup or, best of all, a get up roll, will earn you a few frames of invincibility, so that you won't get hit by the bomb but the opponent will: that makes getting up from the ledge very safe (you lost the second match because you jumped with a bomb that was about to explode).
- Don't waste your midair jump while recovering, so use only Up B when possible: once your jump is gone, Link can easily be gimped.
- Don't get greedy when you're looking for the kill: throwing out Dash attacks and Fsmashes (both ridiculously punishable) will easily cause you to lose your last stock, especially against a character like DK, who can kill easily with a well-timed attack
My general advice for you is to mix up your game, especially your long range game, with more jumping and less rolling. Only throwing grounded boomerangs and bombs, and shooting grounded arrows, will make it easy for the opponent to approach you in the air. Watch how Kirin utilizes short hops and full hops while pressuring with his projectiles, and while pressuring up close with aerials:
https://www.youtube.com/watch?v=zAGBn57C2NM