Lol, as much as I know both of those characters, I would rather do someone that we obviously fear more (Wolf/Lucario/Snake/Marth/Olimar). I have good MU exp on D3, Marth, and DK. So I'll try to give some input on all of them.
DDD -
This can become a boring MU (I see it happening in the future), but some of the CPs Yoshi can pick can make it fun too since he's soo big. Obviously, you want to be careful cause CGs mean 40%+ every time and being placed offstage/on the ledge (which is quite bad for us). You want to bait moves out before attacking cause it's gonna be your main way to getting in good starting damage. From there, you want to mix in Bairs, Egg lays, and pivot grabs to keep them in the air and to keep us on the offensive. Keep your spacing with ETS, and keep DR to a minimum.
If you get CGed, pay attention and mix up spotdodges and Fsmashes. You don't want D3 to match your Fsmash with his or else your dead. As for being on the ledge, you HAVE to mix up from how many eggs you throw to whether you'll DJ up with egglay/aerials or just use the normal getup options. We're somewhat fine when our damage is under 100, but after that, things get really ugly from there (and I haven't figured out ways to help this either).
Keep your Uair fresh for killing at 150%, and use DownB when you have the chance since it'll kill at that same percent too. Usmash isn't worth killing in this MU cause it don't kill till the opponent is about 180% fresh, but don't abuse it cause it's simple to counter if you're playing dumb with it.
Marth -
Have fun using the ENTIRE stage running from his sword. I happen to like this MU more than the Lucario MU since Marth's hitboxes are at least ****ing realistic (Mostly all of the anyway). For the most part, DR works well here since you need to be ready to get chip damage in when Marth misses a Fair. All of yoshi's normal ATs we've been using are used often here (no surprise) but egg lay is kept to a slightly less use. Stay grounded most of the time cause being in te air is asking to get thrown everywhere. Remember that you have DJ through the down version of DB (the multi-hitting one) and learn to SDI DB too (although I suck at SDI). If Marth is one the ledge, leave him be and just throw eggs from a slight mid range. whatever option he uses, we can normally punish it with ease as long as your paying attention.
Oh, and when you get knocked off and you recover high, start using wavebounced egglays to make em miss. If you do the move right, you can sometimes punish them for trying to attack us while you recover (like a reversal wavebounced egglay).
DK -
Power. Why are we afraid of this? The only thing truly scary IMO is Dsmash, which you can block if you stay calm. He gets juggled very easily and he has very little options from the ledge. Patience is of virtue here as he can't compete well with the zoning of eggs and the mixups with egg lay. however, I will admit that walking Ftilt can be annoying. If you happen to get caught in it, just walk away.
When juggling him, chase him with wavebounced egglays incase he airdodges early, pivot grabs/Bairs to abuse his landing, and Fsmash when you can understand the timing for it (I know cause I still fail at the timing for it often). DK's Bair is annoying and unpunishable from a normal SH (considering if you spotdodge, shield, or try to attack inbetween Bairs). Keep your distance and pivot grab it or just don't fight it at all. One thing though, if you can get lucky at timing things, you can probably slide an Usmash to trade hits.
When trying to kill, use DownB when punishing his landing lag, drop off Uairs when pressuring offstage (it kills him well from the ledge), or Fsmashes to punish his lag. Usmash works too, but I don't kill with it often. Oh, and just remember that Dair > Nair/Uair truly combos when the opponent is over 100%. If you use Dair on a shield, then try to Bair to make his shield dumbly small and shield poke, which can lead to a free Fsmash from the hitstun of the Bairs (except the fourth hit).
For the drop off Uairs, I don't have it down completely, but it's an extremely good option to use on him since he's forced to recover higher. If he does this, you can DJ up and Uair him. If you can force him close to the ledge while you grab it, you basically have 1 free Uair on him. It's a great tactic to pressure DK when recovering (only in terms of you trying to kill him).
Lastly, careful when egging from the ledge. Dsmash will say hi, and your stock will say goodbye at the same time.
Pikachu -
I wish I had MU exp for this, but w/e. Tjolts are gonna be common to neutralize the ground. learn to ping them out, but make sure that pika isn't at mid/close range when you're about to do this. You're basically gonna be asked to get hit/grabbed while trying to defend yourself from the Tjolt. For the most part, I would say to stay grounded, and to try using DR to keep your speed. Pika can CG us for a little (20% I think?), after that, we can Nair, but sometimes they'll expect that and shield, so keep that in mind. learn to DI up out of Dsmash, and please god do not airdodge into the ground cause that's when you'll be asking to get Dsmashed. Space yourself with Jabs, Ftilts and Dtilts cause OoS Nair can **** Yoshi, but it's a consequence for using it too much as it's his killing move.
Uair can sometimes combo into Nair so be ready to DI Uair. DI up to get out of Bair, and learn to not ****ing momentum cancel when pika is below. Unless you have great DI reaction, you'll get thundered and lose a stock for momentum canceling. Uh.....if pika is on the ledge, just egg him cause he has two main options that make him hard to punish (QAC and the normal getup options). Plus, drop off Uair will hit us if we try to get risky over the ledge.
Bleh.....Lots of info and I got lazy at the end. Anyway, take this how you want.
Can you elaborate on your opinion on turnips in particular in this match?
