What's really good to do is when your in a neutral position is to angle your boomerang just past their head. This will keep them from jumping at you. At that time you can pull a bomb. Even if they do run in and approach it will stop because your boomerang is coming back. It's a really good position.
Get that boomerang behind your opponent. After the boomerang is behind them, I wanna try to start being more agressive and see what happends.
A promise is a promise so here goes. I am going to be very critical and try to comment on every little thing.
0:03 you do a late nair, don't space it or get near him and he grabs you. try not to approach.
0:10 he Uthrows you onto the top platform, you saw this as a weak position for you so you got out of there, good. Don't try to approach marth while in this position ever.
0:14 The Marth throws out a fair and some dancing blades. You were middle stage and he pressured you, you jumped off stage for a second, made it back on. Even though he didn't hit you he still cornered you. Try to not let yourself get cornered like this. You did do a nice combo afterwards though.
1:19 bad fair, but you knew that.
1:37 you cross him up with a boomerang and have enough to pull out a bomb, that was great.
2:19 you UpB'ed. It would of been better to reverse Dsmash there. But he still died somehow...lol.
2:42-2:52 You got pushed off stage many times. You really need to sweetspot your recovery. Your opponent will always take advantage of this and it is a huge weakness. I think you got a little antsy, went for the fair and died.
2nd match: Great, BF is great for Ylink. (Besides his zair recovery) you can run around on those platforms and make him approach.
3:40-4:00 you stayed on the ledge way too long. You keep trying to attack him. Your in a bad position right now, the first thing should be to get away to a neutral position. You could of rolled or jumped on the stage.
4:25 perfect Dmsash opportunity but you missed your dair
5:04 Dsmash opportunity.
5:10 Dsmash opportunity.
5:34 Your on ledge, you jump up fair and he just shieldgrabs you and throws you off.
3rd match:
6:59 Marth Up b recovers right onto the stage, you just sat there and pulled a bomb halfway across stage. You could of easily edgeguarded/Dsmashed him.
I will critique the rest if you like, but i g2g now.
General advice:
After you pull a bomb you always throw it right afterwards. Don't throw that bomb, boomerang/arrow instead. This will force him to evade those projectiles. If he uses his double jump then it's a free bomb hit. You really want to force things like this, notice them, and take advantage of these situations.
IDK exactly how effective it is vs Marth. I would say to Bair more. It's really good.
You need to punish mistakes with Dmsash, especially at higher %. At lower % go for a grab>Utilt/Dair.
If someone is above your Uair them. It has insane priority and good range. Keep them above you with this. If someone is above you, you usually just nair them.
The Marth you played CC'ed a lot. You can't CC Ylinks Dtilt, I hope that helps.
I hope this all helps you.
This is a video of my Ylink I uploaded last week. It's very recent. Maybe you can take something from it.
https://www.youtube.com/watch?v=otuk1DbTrTo&feature=channel_video_title