Swei
Already have a good amount of things to break down for you if I were to get on every moderate to major issue you did in that match; however, it'll be more worth your time if I were to pinpoint major issues and explain what you need to improve in.
Moving from that, just wanted to say that the MK definitely has major predictable gaps in his game, which you can beat if you get a better handle on Yoshi's tools.
I assume you have tap jump on? Typically it's not worth it for us to use tap jump since egg throwing can make you DJ unintentionally, which is what I keep seeing you do. If you're more bent on having Tap Jump on, then you need to master not using your DJ when trying to egg throw. Mistakes like this are a major hindrance on your game.
From watching you play, I think you're accustomed to wifi lag more than off-line, which doesn't help you when seeing how Yoshi has a few things that require on point reactions (Yoshi's CG to Usmash on MK is one example). I get this because you're constantly throwing out moves in places where you either expect him to be or where he was. There's nothing to really get into here, but play off-line more often (even if it means practicing movement and techniques in training mode).
Stop using pivot grab as a crutch to get your opponent's pressure off you. The move is not amazing and can't be used foolishly, especially since MK can punish it easily. Learn how to manage the bad spots that you tend to panic on so that you don't fall into predictable tendencies.
Your spacing game can use practice. Understand how far Yoshi's range is with moves and where he excels at against other characters (relative range [close, mid, far]). There's moves that we can tell (from an initial standpoint) where it ranks compared to the rest of his moves and what area they cover the best.
When I refer spacing, I mean understand how to play with Yoshi's moves such that you're not able to be punished as EASILY (keyword) as one that doesn't has a move spaced. I can get into more details if you want me to, but just to let you know, the concept of spacing, zoning, stage control, and such is hard to grasp as a whole (especially when putting it all together).
Now moving from spacing, you also tend to throw out moves that don't seem like they have a purpose. Always have a reason to use a move, even if it is relying on a whim. Throwing out moves recklessly places you in positions where you're going to get punished (as shown in the match when you took tons of damage and flew all over the map). Next time you play (excluding wifi cause I never opt wifi for practice), try to think about giving a reason to why you threw a move out. You'll play a little slower as first because you're not used to it, but it will help in the long run because then you can focus on adapting to your opponent's playstyle rather than what move you should use. It should become instinct when you gain more experience playing and learning matchups.
Moving from general experience, I'll mention a few matchup issues you need to know about.
I don't know if you realized, but GR > Usmash on MK at low percents is a bad decision since Usmash doesn't push him away enough to keep him from punishing you. Usmash only becomes worth using around mid to high percents. I can't really opt another method since I use DR for my combos, but it'll probably be more worth your time to pummel for damage, and carry MK to the edge without Usmashing.
Don't let yourself be above MK, his Uair covers way too much space (too quickly) for us to punish. Our moves don't cover as much space and take much more time to get out than his, which is why we have issues when people are below us. Not only that, but he can bait out our moves by using his multiple air jumps. We don't have the same ability, and we need to stay below (or even vertically) when it comes to an air-to-air encounter.
Lastly, calm down when you play. You're trying to play as fast as Zudenka, yet you can't handle Yoshi's moveset. Slow yourself down, and learn how to manage his moveset, then speed your game up.
Firefly
You already know I'm going to tear you in two. Prepare your anus.
Spent 5 seconds doing pretty much nothing. You didn't get him to feel intimidated or get any pressure on him. Not only that, but you were open for a counter attack 2/3 times you did something. Either you're going to pressure him up close, or pressure him ranged. Make up your mind though.
Notice how he's just chilling at the ledge and you're pretty much doing the equivalent of a melee player doing a techskill video. Calm down and keep consistent pressure on your opponent. You didn't have any real momentum to warrant that kind of movement, so keep yourself reserved until the time comes.
Wavebounces shouldn't be tough for you since you changed your C-stick to use B moves. I suggest you practice your wavebounces with C-stick so that you can have a much better use of your B-moves (egglay has to be done normally though <3) when creating pressure.
What were you going for when you threw out all the egglays? I'm not referring to the ones that actually put pressure on Wario, but the ones that were just done in place randomly.
Downsmash isn't worth using offensively. You did good using Jab at 18:57, but you should've used it again at 19:02 since it gives you a chance to place better pressure on his shield, and possibly stuff his OoS option (with 2nd jab for example).
DJAD isn't the best option as often as we tend to use. Wario isn't like MK, where we need to DJAD the moment he gets close to us while we're falling. Remember that Wario has practically the same air speed (and even better acceleration) as us, and because of this, we need to utilize egg toss more. Heck, you could've went slightly under the ledge and instant ledge snapped using the C-stick (or B-stick if you want technical terms) before Wario had a chance to attack. You have easier inputs to getting recovery options that we have trouble with, and you should definitely use them more to keep yourself from taking damage while off-stage.
Great job on his 2nd stock. You played that extremely well; However, as soon as he started getting a few Dairs on you, you tried to get away. Do what I tend to do, "Jab first, ask questions later." Soemtimes it's not the best choice, but it can definitely help you slow down your opponent's momentum if he/she's pressuring you hard.
Don't chase too hard, especially on Wario. You're better off limiting their choices and forcing them to make a panic decision that gives you an easier time punishing. When you're being too aggressive, you often place yourself in a bad position, which lets your opponent punish you and/or get back on the stage freely.
Play vs more Diddy or practice using items and comboing into them. No need to get into more details. Having a better handle on items will help your vs Wario, Peach, and Diddy (maybe Snake).
20:53 is a prime example of where you can jab first, and ask questions later. You didn't scare him enough to spotdodge, so jabs would allow you to force a different option, which would've been a grab or OoS Aerial, which isn't as bad as taking a Fsmash.
You need to practice using your eggs. Most of your eggs aren't helping you limit your opponent's options.
Just noting about recoveries, you chose between doing a DJ egglay or DJAD for two and a half stocks before using downB to get to the ledge.
Lastly, there were times where you believed that he was going to land on the platform after your grab released. If you believe that he's going to land on the platform, you can FH Dair his shield to place more pressure and allow you to shield poke if you end up on the offensive still. Usmash is still a good choice since it pokes through the platform and can possibly push him off the platform and fall onto the ground. Plus, the lag is the least so that it makes it harder to punish.
My closing is to use more jabs man. You started using jabs, then stopped when you got on your last stock. Jabs help your place pressure, and can help lead to combos/kills when you need them. You want opponents to fear coming close to you because Yoshi has that ability.