I'll upload some videos of my MK during this week.
I'm bad at discussing so this is the only thing I can do.

F-air B-air and N-air are all great for edgeguarding
D-throw U-air (Smash 4 tactics)
D-tilt goes well with F-tilt
D-air can be used for approaches (dash, short hop, D-air) N-air and F-air can be used too
THAT NEUTRAL JAB THOUGH!
A very silly edgeguard tool which, can cause opponents to leave them open for an edgeguard (though that only happened a few times with me)
U-smash in turbo mode can infinite combo by cancelling the u-smash after the second hit with another u-smash
I'm done

D-throw uair isn' really great: nair is better, and with good DI uair won't connect.
Jab is one of the worst moves in the game because an opponent can mash an attack before you can get out of the jab

D throw to f smash is pretty good at low percents but you have to read to DI.

Just picked up this char thinking Brawl MK strats would transfer over, and they mostly do.

However the way I play MK is pretty lame right now. Any tips on how to use rushdown with this character?

F-Air and N-Air work well. Reverse Aerial Rush B-Air is nice if you want extra range.

Wow, Meta Knight is going great for me so far.

I rarely use Down-B with him though. I know it's a kill move, but I seldom use it. Pointers on using it effectively?

You don't have to force yourself to use it lol; it's somewhat situational of a move (comparatively). It has high Knock-Back and can hit people below you and to the side. Not as great as his other Aerials, from my experience back when I Mained him.

Glad you've found a second character that you're comfortable with, and they even seem to compliment each other's Match-Up's quite well. Congratulations ^__^


EDIT: NVM lol I thought you said D-Air:V

Use down-b to counter-edgeguard (the opponent'll most likely stay on the ledge) or when you're 100% sure of the opponent's position.
Don't use it to end a combo, it's not worth taking the risk. Also keep in mind that it'll not kill heavy people under 120% (140% if they DI).
I only use it against Marths since I'm not afraid of their punishes + he's floaty.

Dimensional Cape is also useful for tech-chasing if you don't think you can JC grab or something before they can act out of the endlag. As a finisher it is extremely situational, but useful if you practice and think you can pull it off. It's rarely punishable even if you miss it at the end of a combo, so if you can't reach them any other way going for it might be a good idea.

It's also a great recovery, so become good at sweetspotting the edge.

I never knew that jumping off and using Bair, then grabbing the edge again is called planking. It's been really useful for me to keep most pesky edgeguarders away; Bair has quite some reach. I also keep myself in the air with multijumps right next to an edge to discourage approaches with Bair, and it works almost every single time. All I have to do is regrab the edge and I can do it again.

I feel like I'm leaving Fair alone, though. It's faster and has a little more vertical range, but it feels like Bair is the better move overall because of more horizontal range and less endlag. In what situations would Fair be the better aerial to use over Bair?

As long as you can't dash turnaround bair fast enough, fair is a safer approach than nair : longer move and better disjoint.
Moreover, since the move has a better vertical knockback, you can use it in combos.

Is fastfalling with the first two hitboxes of Fair/Bair viable? Sometimes I use it to land a few combos, but I'm not sure if it's worth the trouble.

FF Fair/Bair -> Ftilt Combo/Reset

FF Fair -> Dtilt -> Ftilt Combo/Reset

FF Fair -> Dtilt -> Usmash

FF Fair -> Dtilt -> Dsmash

FF Fair -> Dtilt -> Grab

FF Fair -> Dtilt -> Dash Attack

FF Fair/Bair -> Dash Attack -> Usmash

I don't think FF bair into dtilt/fair is possible unless the foe DI in.
If you meant to only hit with the 1st two hits , then FF will leave to your foe less time to break your combo. You might fail if you don't FF.
BTW you should try FF fair -> Ftilt. I never tried this into dash attack. Smart idea.

Just found out how to WoP from 0% with MK, awesome. I alternate between Fair and Bair with each multijump, and usually end it with a Nair or Bair.

There are some neat alternatives for the finishing move, although these will cost you your stock. Drill is a funny finisher that pushes the foe into the blast zone if aimed right, and Cape is a stylish finisher, but it's pretty difficult to land the hitbox that pushes the foe into the blast zone. Shuttle is another cool finisher.

Right now I'm trying to land a WoP with Drill, it's pretty humiliating imo.