For reference material, I looked this up on your match-up guide. I'll paste it here, so you don't have to search for it when using it to discuss.
Week #3
Meta Knight
Match-Up Estimate: 4 : 6
[This match-up is slightly in Meta Knight's favor]
~ Props to Le_THieN for doing a massive re-write
Meta Knight's Advantages:
* superiority in almost every characteristic facet imaginable:
o speed
o range
o priority
o aerial mobility
* very small hurt-boxes
* disjointed hit-boxes on virtually all attacks
* boasts the longest, safest, and most versatile recovery in the game
Diddy's Advantages:
* bananas out-prioritize every single move in Meta Knight's arsenal
* can arguably kill with successfully-landed KO moves at earlier percentages
Specific Match-Up Points:
* Meta Knight's Shuttle Loop is, best to my knowledge, still in the running to be named the absolute best special move in the game. It is a special attack that combines blistering speed, high priority, and an absurd amount of knock-back at low percentages that not only makes it the perfect anti-air and anti-edge-guarding tool, but also doubles as an ideal off-stage gimping resource.
o On top of that, it has at least one frame of super armor during its nearly nonexistent start-up, and automatically places Meta Knight into a gliding state - setting him up for a glide attack equal in priority and power.
+ If the glide attack is executed near the ground, it can be lag-canceled into any number of Meta Knight's other, near-lagless ground attacks. This makes this possible three-move chain virtually unpunishable.
* Meta Knight's fast ground speed, high-priority special moves and plethora of ranged, disjointed attacks all grant him the ability to quite literally crush the spacing of every single character in the game.
o Additionally, Meta Knight has absolute aerial superiority in every way. Aside from a ground game that shuts down most other characters' abilities to safely approach horizontally, Meta Knight is even able to administer a ridiculous degree of pressure by vertically spacing with his fast, ranged and lagless U-air and D-air.
* All four of MK's special moves grant him some degree of significant mobility; this effectively grants him four different recovery options.
* Most Meta Knight mains will stay in a constant state of flight and zone from the air in order to decrease the effectiveness of Diddy's banana approaches.
* Diddy is very, very susceptible to Meta Knight's off-stage gimping game due to the vulnerable nature of both the charged and blasted states of the Rocket Barrel Blast. If Meta Knight intercepts Diddy at any point of the Rocket Barrel Blast, Diddy is almost as good as dead.
Strategic Notes:
* As previously mentioned, there is one trump card that Diddy has over Meta Knight (as well as the remaining entirety of the rest of the Brawl cast) that he will never be able to beat if they are effectively deployed: bananas. Combined with unique ability to readjust spacing with glide-tossing, you will always be able to quickly capitalize on a Meta Knight who enters a tripping state or a short banana hit-stun state in the air. The smart, measured application of bananas in this match-up will ultimately determine which direction the favor will swing in; it's therefore imperative that Diddy has bananas out at all times.
o The Mach Tornado is one specific move that MK mains are fond of whose respective cool-down frames can be taken advantage of with glide-tossing. Diddy has surprisingly diligent shield endurance against the Mach Tornado, and he can immediately glide-toss out of a shield in order to punish the Mach Tornado's period of cool-down.
o Similarly, D-smash is easily one of MK's most used and abused attacks due to its blinding attack speed and strength, as well as nearly nonexistent execution lag. If I recall correctly, the second hit of the attack actually has more knock-back, so expect to see a D-smash if you anywhere in range, especially from behind. Use prudent positioning in order to get behind him and bait the move - even with slight shield-stun, there is still just enough time for Diddy to get in a glide-toss before Meta Knight can spot-dodge or get his own shield up. Even if the timing is whiffed and MK manages to block the banana, make sure that you always glide toss forward in order to close distance and quickly follow up with a grab.
* If Meta Knight takes to the skies, do not even attempt to go head-to-head with any of his disjointed aerial attacks (unless you have a banana in your hand or you are punishing a whiffed attack). Hit, re-space and run by harassing Meta Knight while he is in the air with a salvo of peanuts varying in height and jumping banana throws in order to bring him back to the ground.
* Surprisingly, Diddy has a diverse array of options in order to interrupt and override the Mach Tornado:
o Banana Peels
o Diddy Hump
o F-tilt
o fast-falled N-air (above the whirlwind)
o Rocket Barrel Blast (you must allow yourself to be hit during the charged state)
The Diddy Hump and F-tilt in particular require a high degree of spacing awareness and directional anticipation of which way Meta Knight will go once he has activated the Mach Tornado.
* For as excellent as Meta Knight's overall recovery might be, Diddy has the distinct advantage of having the superior recovery that combines the longest and furthest horizontal and vertical trajectory – with, of course, proper aerial spacing and enough of a barrel charge. Meta Knight mains who are aggressively edge-guarding you will almost never chase you any further off-stage if you actually jump or Monkey Flip backwards in order to adjust spacing for your Rocket Barrel Blast. By that point, you will already be charging your barrels to maximum charge, and the slow descent of your charged state will position you off-stage in such a way that you are actually too low and too far away for Meta Knight to gimp you and recover himself. It takes some practice and precise directional influence, but it is logically one of the safest ways to recover without putting yourself in immediate danger of being directly gimped.
o If possible, it is worth the effort for you to bait Meta Knight some distance off-stage before you re-space by jumping backwards. Opponents will then be faced with the dilemma of pushing onward with the chase (in which case they will also face the higher probability of death), or simply turning around and flying back on-stage. If they choose the latter, you occasionally score free damage by to rocket-barreling back onto the stage, but not before you blow through an actually helpless Meta Knight.
* The Drill Rush is easily escapable. You can minimize the damage it inflicts by smash-DIing through it.
It's 50-50 on alot of stages, the ONLY way metaknight can possibly have a 55-45 advantage is from gimps. Everyone who doesn't know what they're talking about shouldn't come in here and pretend they are giving out "helpful" tidbits about the ratio. Diddy wins on FD, diddy goes even on smashville, ps1, battlefield, and possibly the other neutrals. He is 45-55 everywhere else.
