Okay, so last night I was teaching people and I had a lot of interesting new thoughts but I only remember a few. Actually, some are new and some are just fundamentals people need to appreciate more.
When someone is on the edge and you miss your aerial (or are in lag from whiffing a move etc), it is essentially the same situation as when someone is standing beneath you on a platform. It's a guaranteed hit/combo for them so when you approach the edge, always be spacing (duh) and not forcing the situation when you should be at advantage (stage control), especially if you have good range. The best edgeguard (to start) will always be to cover the fast option then reacting to either the kill or them catching the edge (wd back and try to bait an aerial or ledge dash etc). Spacies' pivot bair after they catch the edge to beat the immediate rising aerial (vs most characters) is too good.
Falco's best vs Marth is bair, for spacing, for getting him off the stage, for combo'ing (weak bair <3). Force Marth above you and always stay under him pressuring/punishing with bairs. Falco's jump height and fall speed make it SO SO good. Chipping away with bair's stacks damage fast. Fade out bair OOS is so good too, especially for not getting grabbed out of shield pressure, but is riskier vs characters with OOS options that have a lot of range.
When using spacies, utilize the shine, if you haven't double jumped already, after you come out of lag from doing an aerial (FH bair for example) and then shine close to the ground and use your double jump to either space another aerial (since they likely thought you'd land first) or waveland to shine/aerial/laser. Basically, if you don't land, you aerial sooner and it messes with their timing. The fact that you can shine turn around waveland after jumps gives you even more options for switching up your movement.
Falco's SH first hit fair hits through/pokes feet on BF, YS and PS. If you can combo them onto a platform above you, shuffled SH fair can lead to dair kills or at least continued combos. It's best because it's fast, underused, and it's relatively safe (mid combo anyway).
Not shining after Fox's aerials (if they hit) is **** and at very least an amazing mixup because Fox (other characters to a slightly lesser extent) because grabs after aerials tend to set up for way more than just shines (shines can be DI'd away or DI'd down and teched). Not to be used in every situation but good to mix in with SH uairs, SH bairs (higher percents), DJ dair (beats get up attack) and shine waveland to whatever.
The most important part of a combo is the part where they are off the stage but above the edge. Try to move to a position where it looks as if you are too far away (great with Falco since his FH is ****, bair's disjoint/dair trades etc) and then **** their jump/air dodge. If they haven't been jumping straight out of hit stun (which is great sometimes if you're really high up, extra height = extra horizontal and more chances to live), then do something to catch them/bait them out of fast fall. The point is to be ****** them if they are jumping, adapting if they aren't, but always making them have to focus harder on a combo they likely thought they were out of. Combos aren't over until you are combo'ing or they are dead.
Air dodge is an amazingly good, lagless third jump, especially if you can get the last part to wavesomething onto a platform to (angled) shield or light shield. So many times people do a decent combo and have to up B/side B/anything laggy afterwards and they lose their advantage/positioning, miss combo/kill opportunites, or get killed themselves (this happens more with dumb Falco/Falcon recoveries).
This is more obvious but PS's transformations are amazing for characters with linear/laggy recoveries (Sheik, Falcon, Ganon etc) because you are given an option to land on platform and then either try to shield/spot dodge or (what will likely happen) get hit and DI/tech. Getting hit and immediately tech or even just DI'ing down and get knocked to another part of the stage is infinitely better than dying, obviously.
If you are tech chasing, move to the spot where they tech and react. This is so basic but so many people don't do this enough; it just makes sense. If they have four options, two of which are covered by hitting where they land, the other two being their rolls either in or out, then a fast character should easily be able to get a grab/hit, and it's even better with a character like Sheik whose dash attack is also one of her best launchers. If you predict the tech, you will get a **** punish/combo/kill but if you miss you lose your advantage. Reacting vs Predicting is low risk vs higher risk. If you can tailor your reactions to make them eventually do the tech you're waiting for, you will get the most damage and likely your kill. iIt's all about tech chasing/reacting faster than who you are playing and keeping them guessing. If they are being predictable with rolls, by all means take the predictions and **** them.
Related to previous, close up spacing/solid shield pressure is just as much about getting people to overcommit/jump/roll than it is about actually hitting them with the pressure. If you're pressuring with Falco, it's better to dair/dash attack/fsmash/dsmash their roll than it is to get a shinegrab (most the time though this is preference). The longer you pressure, the more chances they have to shield DI, shield grab or **** you OOS. Falco's shine's range sucks so either make sure it's hitting their shield (hitlag<3) or immediately fade out with nair/dair/bair. However, even if you're pressuring near perfect, almost all of the top tier has a deadly response to Falco's pressure so you have to be fast and mixing up fast.
EVERYTHING in this game works and NOTHING in this game works.
I'll add more in a bit.