Spacing is good and all, but spacing is a part of everything we do as Marth, To the point that I don't think it should be classified as the 'technique' as much as the implied mindset/movement that goes into
everything you do as a Marth player. Even our close range confrontations are spaced to out do their grab and out of shield options and getting things due to that pressure (don't tell me players who use Marth's dash don't fully take into consideration the lengths/etc he needs to start / time those actions [and out of dash options exist !]).
With always considering spacing, some of the prime things Marth players need are
Timing - Buffering shield drop turn around grabs, buffering dashes out of aerial landings to get better follow ups / apply pressure "as fast as it can get", knowing when to aerial and when to jump/etc and how you walk and talk and etc. Dash to shield is 17 frames, even if holding shield while in neutral will auto-do it for you.
Pressure - always think about the next two actions your opponent will make. If you don't know the match up this is hard but it's the bare minimum. Against some characters (i.e. Toon Link) you honestly need to think of their next three steps. Better/high level players delve further. A really good understanding of your options, your hurtboxes, your hitboxes as well as fluency in movement.
If you don't know a MU (as well as them) against a competent player who does most struggle to apply pressure and lose; you don't understand their options nor how yours work against them, you'll often fall back to a "safe" idea (in my case spacing neutral airs) and against players considerably better against you this stuff fails too.
Without pressure you're likely to have gotten yourself gimped and it likely started out of a power shielded dumb forward air.
Mixing Up - Marth has a lot of good options and whilst some are godly (Neutral air), you need to be more well rounded in application. Marth's best options will often lose to other character's best options in common situations (even in a broad sense as simple as getting power shielded). If you were spacing better things may have worked out though, right? But it's not always possible, and when it is - you generally are in god mode and who gives a **** about them gangnam style. But definitely not always possible, better players manage their movements in a more precise manner, hence to keep up with them you need to do so too, even then it won't always work out so you need to MIX UP.
Tangent aside, Marth's best option may not beat the other character's best option in the situation. However, another option Marth has is likely to cover some things/save your life.
e.g. If you're perfect spacing pro, Meta Knight won't shuttle loop you to death as whenever he does it your sword will swing and hit him whilst whiffing you. God mode. You're the Mr ShaynairneomiiikooHAZE.
BUT SUDDENLY, you're back in reality and air dodging is stupid. MK's know that you're likely to air dodge or somehow try to punish them (actually, they don't), so generally they wait for the air dodge giving you time for...
FOOTSTOOLING and actually hitting them with aerials, my gosh you caught them shocked! A FOOTSTOOL DOWN AIR!? Next time though, this MK DOES IT AGAIN AND YOU- wait reality, they're gonna just shuttle loop early next time and **** you if you try that **** again. Get where I'm going?
Practising mixing up is good in friendlies / during training with someone around your skill level (high level can work but most are illiterate, amirite?
; this is because they tend to intrinsically react to your **** as you do it and punish your mix ups anyway) and tell them things they're missing out on doing
CONSTANTLY, and try to get the same in return.
All these things kinda gel together and overlap a little. There's likely more to it as well. But when I think of times where I lost to people it always comes down to those three things in my mind (or sometimes flatly "I was terrible at spacing" [i.e. I was bad at life]). Against the high level players you lose in all 3 facets and they also come with a super special ability (like 10 frame reaction speed or using Ice Climbers). Some players actually are as good at some facets as high level players but generally do worse in the others. Really good Falco players could be tippy top technical and be a gliding smooth mother ****er and not know how to mix up and do considerably well.
