Some facts/thoughts/strategy that might not be known by everyone
He is the second-lightest character.
For everybody that isn't aware yet, autoland nairs are awesome. If you combine it with the PM close-to-the-ledge stand that is basically an onground ledgecancel you have no lag at all. Drop againand repeat or choose another option.
Up-bs edgeguarding efficiency isn't explored yet. The key is to run off, fastfall, jump in the other direction and then up-b (in the initial direction, so facing towards blast zone).
Partly mentioned but side-b/down-b ledgecancels. Instant down-b OoS is also underused.
Applies for more characters than just MK but RAR aerial ledgecancel ledgegrab is cool. Nair and bair work best for covering multiple options.
Up-air followups based on horizontal momentum: As known, successful attacks' knockback angles aren't dependent on your momentum, so you will get the same angle while you are positioned differently. A forward jump up-air -> bair or a backward jump -> cape might be easier to set up that way.
Meta Knight has many sneaky reverse hitboxes that are difficult to get but very rewarding. While the fair one is rather annoying (opponent can SDI in to get sent in the other direction), the bair for kills and the d-smash (really really hard) to combo in its own second hit are examples where it makes sense.
Applies to almost everyone, but the effect of jump starting horizontal momentum and pivots aren't known or used widely enough.
The strongest empty cape is the crossup one, all others have huge disadvantages.
Zero-Lag-Cancel: If you land below a certain speed and right after ending glide you will not have lag at all. Sometimes useful in general, sometimes as glide attack mixup, but don't get gimmicky with it.
You lose quite a lot of mobility when relying on midair jumps too much, they are only 50% as high and horizontal air traction is applied throughout the entire process. Low % combos with up-airs are worth it though.
MK goes into his run-animation quite early.