I believe i've posted more in-depth explanaitions in the DDD boards repsective matchups threads
but vs
ICS:
Bair approach, once in, dair camp, footstool and dairs, one lands on sheilds insta-pokes (two shields and a strong rapid hit attack greatly deminishes the shields further) IF they somehow didn't poke, u can jump again/footstool away, or dair again, def. poking at least one, seperating them.
Once seperated DDD has some of the best "keep sepereated" game in the game. One being plain grabing each as they try to get near each other, bair spamming, or charging things like dsmash.
Also if u think they continue to hold shield and are afraid of them uaring out of shield between dairs u get free mixup with inhale, if u instantly spit it out it's gona hit the one u didn't inhale.
HOPEFULLY u inhalled popo so at worst the quick punishment is a jab or something.
Bairs=easier gimping capabilities than mk's dair, as it flat out can beat IC's side b, sending them far back off, and lower at low %. also charge sidesmash is nice here, the range and power on that makes it easier to hit, something mk's fsmash lacks (i often take the side b when i try to time mk's fsmash to hit them off)
and if u grab one (right next to the other) i like uthrow instead of foward
its fast enough u can throw one up, it pushes the other back, u grab the other, throw up into the other, air chase original, repeat (also easy seperation, but don't look for grabs its risky as balls)
There's also the factor (don't know if u count in in the meta gameness of the matchup) that ddd is harder to inf. and takes longer to kill=more chances of messing up.
Only "gay" thing about the matchup is the edgeguards to be honest.
No IC's do it vs ddd cuz they're dumb and i may be regreting saying this.
All they gotta do from a grab is take to the edge into a fair spike, and grab ledge, wait for up b as nana still has ledge, get up, grab it, new grab inf. or fair spike again (keep in mind ddd doesn't get any jumps back in this process)
but yea, thats only one real advantage IC's have in the matchup that I see being a problem. And THAT assumes the DDD got grabbed to begin with.
Then if DDD does get a lead I feel he's harder to approach while platform camping than MK, but that's just me and my experiences.
OLI:
One simple thing that throws this matchup into ddd's favor, though slightly, is inhale.
It beats 80% of oli's move set, including run up grab (lol) and sometimes pivot grab depending on ur placement and which pikmen it is. It's also a really good edgeguard solution to Oli's down B, throw off stage, turn and prepare to bair, if the oli jumps at all, than tries to time down b for ur bair, DDD can just reverse inhale instead (land on stage) walk off, (provided oli isn't mashing out fast) and spit semi-low (or higher depending on amount of pikmen) Oli (though ddd landed) does not get his jump back and depending on how low you got, most likely wont reach the edge with up-b even with full pikmen.
anything close range get's beat by grab, d-throw tech chase is easiest in the game, and he dies early.
Nair/utilt do a good job of breaking off multiple pikmen attatched to you in one to two hits, and as for an approach treat it like IC's. Bair approach (if they side b'd u alot nair some on the way or ignore) then once close dair shield/inhale ALOT (beats 80% of the **** oli can do at this point) and his roll is so bad he sometimes can't get away even if he were to predict it.
Pikachu:
this one is best left to vids i'm gonna have up in the next couple weeks. its still in testing process but from a sudden shift in playstyle i went from getting three stocked by esam, to borderline always beating him. and threestocking lesser pikachu's. (esam lives down the street) all it takes is for the DDD to NOT play like DDD, and I suppose more like a MK would vs IC's. Platforms are your friend.
if there's any questions, i'd appreciate them to be directed to my PM box instead of a post here, as I don't like checking up on such reply happy threads. (to time consuming)
hope i've helped, even a little.