opo:
Ban: FD, YI
FD: As ICs I generally don't playing on FD because I hate approaching solely on the ground (having to outspace my opponent) but against Pikachu this isn't a problem due to his lackluster range. You have no platforms to run to and your only escape is the ledge or a QA above them, which can spell trouble if they interrupt it (Phantom lag/RCO lag sucks, bro). It really doesn't matter what the other 2 bad stages are since FD is by far the worst and should be instabanned, but I'll go over them anyway.
YI. This stage is pretty abysmal for this MU. Yes you have the platform to run away to, but there is no feasible way to damage the ICs without being extremely risky or using a laggy move which can be punished by (insert aerial). You can't shoot T-jolts down to poke at them because the platform will get in the way. Yeah, almost as bad as FD (You still won't get grabbed, although you will just get hit more).
No other stage is really
bad in this MU but there are clearly preferable ones.
CP: RC, Brinstar, PS1
Rainbow Cruise is one of Pikachu's best stages, as well as one of IC's worst stages. You can camp the boat (right side) with T-jolts and it is hard for ICs to really approach unless they are going to do some really obvious jump air-dodge to land on the elevation. Either way, be ready to get out of that situation and run to the left and just edgecamp for a little bit. On the part that goes up, try to be below the ICs. Being above them will grant you some T-jolt poking, but you need to do ALL of the work on them at this part. Separate and kill nana (She is surprisingly good at surviving when going up, so never assume she is dead). Most smart ICs will just squall up as high as they can and be prepared for thunder so you can't really separate them. At the top part (after the pendulum) your job is to run away. ICs are really strong on the top part due to the fact that there are walk-offs. However, you can be a little ambitious and aggressive on the donuts (or whatever you want to call the falling platforms) because the ICs will not be able to dash across and CG (I will test to make sure) because the block will interrupt them. You have enough platforms to run away at the top, so you should be fine. Either way, you can expect high level matches on this stage to time-out.
Brinstar: One of the few times you shouldn't ban this stage is against ICs. For once, we don't mind the lava or the slants since we don't gain anything from them in this MU anyway. The lava can and will interrupt CGs. Try to learn the lava timings (it is the same every game) so you can now when you can go in without fear of dying. The size of the blastzones is more beneficial to Pikachu since ICs, in theory, kill you from a grab regardless of stage size while Pikachu doesn't. If you separate them and lava appears, it will make the %s of nana and popo differ by even more, which is good for whenever we get a hit.
PS1: PS1 is a good stage to take ICs because, realistically, we are trying to avoid as much conflict as possible and PS1 gives you transformations for 30 seconds out of 2 minutes (or something like that). The platform configuration of the neutral segment gives us ample room to throw T-jolts as well as run away with QA. Nothing too special here, just the basic MU with a stage that allows time to run down for free.
Some notes on stages that will probably be brought up:
Lylat: This stage isn't too bad in this MU. I played terribly here against Kakera and my T-jolt spacing was pretty off, so nothing I did was effective. THe stage gives you A LOT of room to run, but you have to place your T-jolts way better than most stages.
Frigate: I'm personally not too fond of this stage as Pika in this MU. The first part is only beneficial if you get one of them off of the right side, but it causes more problems for you (you have to recover on stage safely with an ICs right there, GL) than it does for them. There isn't much room to camp, the left platform doesn't assist you with safety too much, and they have really strong ledge pressence on this stage in particular since there isn't a platform you can run to far away. The 2nd part is TERRIBLE for Pikachu. You gain nothing from controlling the center while they gain a lot. The platform is similar to Yoshi's considering it doesn't help us at all while it still allows for pokes. I would say don't do go to this stage, ever. Thankfully, ICs generally won't CP it (I honestly love the stage as ICs)