No comment...
As much as you love Dair's, I doubt it will work in most situations as a Edgeguard. Again, Yoshi's Airspeed compared to MetaKnight's, Yoshi can easily just breeze past him with a airdodge.
I know, I know what MetaKnight can do
The main problem is that Yoshi can't Approach MetaKnight worth crap. Bair, his primary approach, gets beaten. His Nair gets beaten. Fair is out of the question. Dash is predictable as hell, Egg Roll is just stupid to use, especially against MetaKnight. The only decent one is Dair, but even that has his flaws.
But Yoshi doesn't need to approach. MetaKnight is a Melee based character. He HAS to approach, the only time when he can play defensively is if his opponent is approaching, or the other character is also Melee Based, and waits for him to come to you. Yoshi has a Projectile, and can make you go on the offencive whenever you like it or not.
Well first thing is to get him onto the offencive. He's going to know what to expect so he's probably going to stand his guard. Eggs works well if he's far away. Well spaced eggs can do a good job, but if you don't space it good enough and throw one when he's too close, then MetaKnight can just move in and attack when he's open. A Perfectly spaced Egg Toss can give it the illusion of what appears to be an opening, but has enough time to react, Pivot Grab, and most likely to catch him off guard.
I guess the most common scenario is when he's mid distance holding back. Obviously you can't use Eggs (and really wish he still had the drop egg's from Melee). It really depends on the spacing, where MetaKnight is, what he's doing, and what you can do. Baiting him into an attack is probably the best tactic in this case. Using an action purposely to leave yourself open, but not something long enough that he can get an attack in.
And then there's the ones that just go straight into him. I can see by looking at MetaKnight closely, and if I see an irregularity in his movement, then I can see what he will do. Proper spacing is the key. Normally using it at max range doesn't really work well, as MetaKnight will most likely telegraphically anticipate a Pivot, and Spotdodge. The good time to do it is alittle after it's maximum range, then you can see if he's Spotdodging or attacking. If he spotdodges too early, he can be punished for it. On the extreme, you can actually space a crouch, fool him thinking you're doing something (Remember, this is split second decisions here), Causing him to Spotdodge, and Punish. I'm not sure if it will work with a Legendary MetaKnight, but it has tricked the good local MetaKnights in my town a Majority of the time (My town consists of Me, a Yoshi user, My friend, an Marth User, Some dude who uses Falco, and about 11 different MetaKnights).
You can't really deny that it takes alot of effort just for MetaKnight to get an attack in. But I guess the same can be said to Yoshi maintaining a stable defence.
That's pretty easy, as Yoshi has alot of inescapable moves..... Ok, 3, but most people only have one! Anyways, Since half his defence is Pivot Grabs, he's obviously going to grab him alot. Chaingrabbing helps racks up damage, but only on either flat stages (Final Destination, Smashville), or Non Platform heavy stages (Halberd, Yoshi's Island, Normal part of Pokemon Stadium, Some parts of Delfino). The Release Grab to Fair Spike works really well, and can kill at very low percents. However it only works if the positioning is correct, which is hard to do on Platform heavy stages. He also has another Release Grab off the ledge into an Nair, which kills at 80% Fresh. This doesn't require positioning.
Last is his Release Grab to Usmash, which can be used at any stage with correct positioning. Now, being that it's the Usmash and more commonly used, he's going to have to refresh it. I think Chew damage refreshes (Forget), but he can also mix it up with a Dash attack or Egg Roll on release. Egg Roll also works really well gathering damage at Low Percents. If all else fails, he still has his Uair, which can kill MetaKnight also pretty easily at a reasonable percent, but he actually has to work to get the hit.
But if you want impressions from someone who actually played people like M2K, you should speak to NC1 Pride. I still think he's borderline even at the least.