Situation-specific critique:
0:27 What C.J. said about giving up stage control. This happens beyond this point but I'll just mention it here.
0:30 spotdodging habit.
0:36 Not sure why you rolled behind him here--I'm assuming missed input.
0:55 good crossup imo. Could have maybe gone for Dair after? I didn't see any attempted Dairs from GR, so I'm just thinking you need to work on that one.
1:22 Fsmash was not the best option here. DB if anything, but he was already shielding.
1:39 makes me laugh. Counter? Don't go in there?
1:50 you were very vulnerable here. Uair has a lot of cooldown lag and should always be used FF'd if you're near the ground.
2:30 not sure why you Daired here but you lost a stock for it.
3:02 Upsmash would have been a good option here.
3:04 Upsmash was not a good option here.
3:06 Should have just finished your DB.
3:31ish You gave up a ton of stage for no reason.
3:44 Spotdodge habit.
4:17 " " .
5:11 Try not to use your second jump so early, and especially try not to land right next to your opponent. This alone probably cost you the match.
5:54 terrible DS. Not sure why that happened. I'm thinking your nerves got the better of you this set.
5:59 again, landing right next to your opponenet w/ an airdodge. Just take the ledge and be patient. You took 26% for that.
6:12 you had RCO lag here and took a Dsmash...ALWAYS do an aerial before you land after you've Up-B'd to the ledge to get rid of this ******** lag.
6:30ish Good patience at the ledge but you had terrible DI and should have lost your stock around 6:35.
6:48 Pivot grab could have been good here.
7:00 You should be WALKING mostly around this part, but generally walking is really good w/ Marth.
7:06 Why pivot grab?
7:14 Good Dtilt.
7:19 Good Up-B.
7:23 Random smashes again, like CJ said.
7:35 Could you have DS'd earlier?
Overall, this is just some specific situational bat habits I noticed. Mostly the random smashes, spotdodging, jumping into the **** w/ airdodges, and letting yourself get gimped. Hopefully this was somewhat helpful.