On the whole, you dodge roll unnecessarily.
If it's friendlies, you don't camp as Link. That's just gay. I watched the Link-Pika one, by the way.
Don't ever U-Smash when your opponent (especially especially Pika, but also Falcon) is behind you. You are left ridiculously open. In fact, you should only ever U-Smash if you're sure of your prediction or made a chance for yourself (a SH U-Air/F-Air that landed, for example).
You use D-Tilt too much. Sure, it's fun, but there are lots of other things you could do.
Never use Up-B on the ground in the **** tent. The rebounds work against you, and they'll have teched before the animation is over.
Next, smash-throw the boomerang more. It's just that much more effective, sans in the **** tent/some edgeguarding situations.
Use D-Air and U-Air a bit more and F-Air a little less. You seem to throw F-Air out a bit randomly while falling...D-Air is a more constant hitbox at only slightly less power, while U-Air has a bigger, constant hitbox.
You should never recover prematurely as Link. There is simply no reason to, unless you feel you have no chance at making it and can hit someone with the move. Also learn to maximise your recovery - once you went straight up before moving towards the stage.
Finally...you have to learn when to U-Tilt. You followed up with an F-Smash several times when an U-Tilt would have chained into 3 or 4 more (you were in the tent, actually, you probably could have gotten a grab or two and even gotten to an edgeguard position). On the other hand, don't U-Tilt too much - hitting a shield can be dangerous
PS: The bomb recovery could have made a difference at 4:15 on that vid. Learn it.