I'll start with Lucario. ISSDI. Seriously, I don't care if people say it's hard, or not worth it, or whatever. It makes quite literally every single one of his moves *with the SOLE EXCEPTION of footstool dair) unsafe on block, at EVERY PERCENT. It's really easy to ISSDI his moves because of the decently large amount of shield stun. Additionally, if you play like I do, rack damage to about 50% with aerials (always looking for grabs of course), then camp. It makes Lucario approach (just ice block his projectiles and laugh). After he starts approaching, it's easy to get the grab. If you end up with a Lucario that is still playing super safe and looking for those dairs, don't be afraid to just uair him to a million, you should be able to avoid his smashes, and they don't separate you anyway. Uair kills eventually, even if really stale, and you can often catch a back air when they try to airdodge a uair, and you'll get your kill. I see this as a 65:35 MU for ICs.
I have Diddy at even as well. We also agree on MK, Marth and I think Falco is closer to 65:35 but that's not a huge disparity.
ROB loses to ICs, but not badly. 6:4 IMO. His projectiles aren't particularly impressive or effective. If you get a gyro, hold it and pressure him to the ledge, he'll have a lot of trouble getting back on stage if you properly blizzard wall him. If you force ROB to upb (easy enough, uair uair bair), he can't airdodge out of it, so just jump towards him to force an aerial (most ROBs nair) and then hit the lag with a strong aerial (one of the best uses for fair). Most of his grounded moves are punishable OOS with something, even if not grab. You can consistently grab dsmash if you ISSDI, or just run up and shield -> spotdodge it. This is one of the MUs where I like fsmash as a punish a lot.
And, ah, Toon Link. I will never, honestly, understand why people think ICs lose to Tink. It's easy enough to trade your uair for his bomb damage, and that's positive. Just focus on hitting him and maintaining a lead. Once you're winning, his camp game is ineffective at best. Only take gift grabs, no need to be greedy in this MU at all. You can bait invincibombs and bair the end of the airdodge and trade bair for bomb (or even bair AND bomb for bomb). If you're good with items you can set up some good traps using caught bombs and aerials.
I think we slightly beat Snake, but that varies so widely, and everyone has discussed that MU ad nauseum. If you want me to talk more about it, I will.