guys, any tips on how to play as marth in a high percent/close match/tight battle match with other high tiers?
At 90% and above, marth's lack of killing power just irks me to no end. I feel so much more comfortable taking out characters at low % at marth.
Don't worry too much about forcing the kill out. Just play with safe spacing and wait for the right opportunity. Less experienced players will almost always get impatient and throw out a bad attack, and that's your chance to strike with a quick up-B, utilt (floaties), or anything to push them off into an edgeguard (dtilt/ftilt). It may seem bad to keep grabbing shield-heavy opponents at 100%+ and not getting a kill from it, but as long as you maintain control then those opportunities are more and more likely to present themselves, and realize that as long as you're tossing them around they aren't hitting you. Fsmash is where most Marths go wrong. I personally try to never use it if they are on the ground out of lag because it means there's a chance they could shield or dodge it and I get punished. Look for fsmash openings whenever they leave the ground or out of any knockdown situation that comes up. Marth can get a lot of free stock-ending fsmashes just positioning properly after a throw. If they're even remotely close to the ledge, a throw on characters that get knocked down usually means you can stand still and cover all of their options with an fsmash in either direction (though you should try to make punishes in these situations as optimal as possible).
Most importantly, try to avoid racking your opponent up to high %s in the first place. Now obviously it will eventually happen, and in some matchups it probably isn't even that avoidable (Peach, Samus, Sheik), but if you focus on low percent gimps, edgeguards, and DI traps, you can greatly reduce the number of times you have to deal with high % situations. Make sure you aren't going for extra combo damage when you could have opted to knock them off stage and edgeguard. I see a lot of Marths try to juggle spacies all day, but if you watch M2K he almost always makes sure he ends strings with nair to knock them off stage. Even if they don't really go off stage, just knocking them near the ledge limits their options so you can get another first hit more easily than if you had uaired them onto a plat where they escape and can work their way down at their own pace.
I think Marth's DI traps are particularly underutilized. There are a lot of situations where the opponent basically has to guess what you will do. If you are chaining fairs in a Marth ditto and they're trying to DI down and away to get out, try up-Bing instead of fairing. Most people try this but they want to do as many fairs as possible which basically defeats the purpose because their opponent can tell it was the last fair and they start DIing up and in. Do it while they're still DIing away. Worst case scenario, they guess right, have decent enough DI to recover, and now the next time you touch them they won't be at an unworkable percent. If they had started at 20% and gone up to 50%, well you can still get some throw combos at 50%. If you had just comboed them with fairs until 90% and they recover to a plat behind you or get to the ledge, suddenly you are stuck in that mode where you can't do anything off of grabs.