My doug is the pika slayer
That's literally his best matchup except for maybe link. Get at him.
Fr Srs tho, coming from the other side of the matchup, what you have to do is not **** up the edgeguards. They should be really easy, but I see so many mid-to-high level pikas fsmashing too slow and getting hugged, or jumping out too far and getting tricked into missing with an aerial (lol). Every time Dougie J. gets grabbed and tossed offstage, he needs to be dead, dead, dead.
Pick Hyrule. This is a big one. Pika is generally better on DL, but doug's B&B combos (especially from ~10%) work really well on pika on DL if the doug doesn't land on platforms at the wrong time like an idiot. also pika gets fthrow-dair'd pretty well, and that's no problem on DL. Pika >>>>>> doug in tha tent. I'd say the matchup is 55-45 pika on DL and like 65-35 on Hyrule. Big difference.
Don't get spiked/knocked out of up-B. Basically, this is a Rock-Paper-Scissors thing, but if you get predictable (e.g. going for the ledge every time) doug's gonna hop out there and pull his long-lasting Dair. You have to pay really close attention (closer than most pika players pay; a lot of them get complacent with their great recovery) and try to go above him if he's already committed himself low, or to the ledge if he's already way up there in the air. Try to avoid a big laggy landing close to the edge if you can, because often he'll have enough time with his superspeed to run over and grab-bthrow or something.
Don't get grabbed. Depending on the %'s, you're gonna get combo'd, thrown off, or pivot-uair'd. Hop around like the little ***** you are and hit him with some SH aerial, then grab and edgeguard like your life depends on it (it does).
Watch for the Fsmash. It is a technique of unreasonable and inexplicable efficacy.
You probably knew all that, but really put it into practice. Keep a knife by the computer and cut yourself every time you fail to edgeguard.