Welllllllll from what I can tell you heres where pika has issues v diddy
Your guys aerial game is far superior to ours.
you have farrrrrrr better range on the ground
you have better things that you can do with bananas and our glide toss is not very good (in most pikas opinions)
heres where we get you
our aerial strings are better than yours and we can easily punish a tilt/smash on shield with uair -> lots of stuff
Our grab game has more mixups and such whereas your grabs are more for killing
We have a spamable projectile
our recovery is better and our thunder can gimp yours.
Personally, I think that our glide toss is worth mentioning as it goes very far it just has a lot of cooldown. If we catch you by surprise it can lead into grab mindgames or charged smashes if you anticipate and try to spot dodge the banana. Diddy's dair doesn't come out fast enough to beat our uair strings at lower percents, so be careful and try as hard as you can to DI that first Uair or else you will probably get naired afterwards. Another mixup some pikas like to do at low/high percents is either sh or fh uair to ff charge fsmash/usmash. Be careful of this, because if you are expecting a nair and attempt to airdodge and we read it you could be in for a fully charged smash and that is not fun
Tbh, we have to play very smart in this MU though because your aerials keep us grounded at close range and your bananas make it hard for us to approach on the ground, so pikas will be looking for hard reads on your dodges, rolls, and patterns to try and get a small string in there to rack up damage. Jolts are probably what a pika will do at the start, but if you can learn the timing and ps them we have a lot of airtime cooldown on our FH jolts so you can easily run in and punish if the pika is camping poorly.
All in all, you are better in this mu than we are. We cant go in the air as easily, and are forced to rely on reads and dtilt, which has the most range of any of our aerials and has a chance to trip and lead into grabs that we really need. Play safe, ps jolts, dont let us get too close. 60-40 diddys favor.
good stages to take pika to are brinstar, fd, and sv. most pikas love sv and fd, but I think you guys are better there than we are, tho again if you can get us in the air or shark us we cant be as effective so BF may not be such a bad choice. As a rule of thumb brinstar is the go to ban against almost everyone, but if we ban FD instead due to the mu then take us to brin if that stage is good for you guys, but again most pikas auto ban brinstar its truly terrible for our psyche and our hygiene. pikas don't like heat, it makes our fur all frizzy and stuff and no sweat glands means a lot of panting
If you have any specific questions feel free to ask