DDD isn't as bad as snake I feel. Obviously people are finding way's around him if he went from 3 down to place like 7 was it? He's losing ground, and Pit I honestly think has an even match up with him. Pit doesn't **** anyone at a higher tier than him but he goes even with a lot of them.
DDD he out ranges us in melee.. the best thing to do is again stay away from him. Unless you feel confident or know what you are doing up close (like koolaid) on a general basis you should stay away from DDD, what you have to worry about is the grabs. His attacks are surprisingly easy to shield (on the ground) if you manage to get close to him and grab him chain grab his ***. Teach those DD D throw - grabbers a lesson

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I agree with Lenus with what he has said.. I'd say follow up with arrows against DDD. He is a HUGE target when you get him off ground. He falls quite fast so doding your arrows would leave him open to vunerbility depending when he chooses to recover. His Up B is honestly punishable no matter what, if you don't get greedy. You can stay away from his up B when he recovers on the stage and arrow his butt. Overall arrows are your best friends here, just watch out for those waddle doos, because they will block your arrow, but it's nothing a simple jump > arrow can't handle.. just space yourself properly and don't rush in at DDD. He is more approachable than other higher tier char's are for him.
MU i'd say 50/50 DDD has good weight and power, along with his famous grab and range. Only move in on him if you see an opening.. don't go all out offensive on him. He is more approachable than snake is though.
stages to stay away from.. I'd say Battle Field and Yoshi's island. (again I feel these are his worst stages - for starters)
I recommend Smash ville over Final D this round because, if he does manage to grab you it does not last as long. DDD's back air can punish you easily if you end near the edge on Final D and you go under the ledge by accident or something. His chain grab lasts longer as well because of how big it is. Final D is still a good stage, but Smash ville considering how slow he technically is compared to pit. Smashville feel's top choice for him for starter against DDD (imo)
for counter.. I'd say to ban surprisingly rainbow cruise/halberd/delfino. Although you both have the Up Air capabilities DDD has a longer range for it, and he can recover through the stages. Not good if you are trying to kill DDD. Other stages to choose would be any that's relatively spacious. I am tempted to say fire emblem.. but that's also bad on the 2nd stage because of the chain grab off the stage. but then the other parts of the stage(especially 3rd) can work to pit's advantage.. I guess Frigate orpheon is his ideal choice, he can recover under the stage and the chain grabs don't last long..