In the past (as Dark) I've struggled hard against match-ups with short characters, especially ones with good combos and killing potential like pika and fox, but then I realized that it's not as bad as I thought. At first my Issue was that I was going for hop aerials and getting punished because they would whiff and pit isn't really lag free.
But one day I got roped into a glory match with a pikachu and told myself not to jump. What I realized is that we have good neutral options between are jab, f smash, and f tilt. F tilt has crazy range and is great for whiff punishes. Jab + mix up works great. I didn't realize this until recent, but mix up your opponent with jab+jab, jab+delay+jab, jab combo, Jab+throw, etc can open them up for a free f smash because the first hit f smash looks just like a jab, so now they think you're going to delay, block, or what ever you been doing to convince that blocking isn't the option to do, sends them flying into no stock zone.
Once you get the lead side b can help you maintain it. I throw out one and then all of sudden people are afraid to come in. If they premature charge up a smash, side b, if i'm in range, that's an f smash and a stock. Roll behinds: f smash. Roll ins: d smash, throw, jab, u tilt, and dair
Jumping at you, believe it or not. At the range where the opponent would jump to avoid jab and even ftilt, utilt and some good priority because of how low it ducks you. I have my neutral so on point during a match that I accidentally killed someone with at 150, didn't even know the move killed. Besides of up tilt, you can nair, fair, turn around bair/dair.
Up smash is great for whiff punishes because the range of which you can slide with it.
Not to mention dash dancing in front of the ledge. They know you want that f throw, I try to space my dance so that I come out of it with a pivot grab to f throw them anyway, forcing the jump, which pit has many answers for.
Dair timings are important. I started knock opponents off the stage into a new game where every time they got knocked off I would be come that much closer to spiking them until I make some crazy dair your that sends them to no mans land.
It took me forever to learn how much of a fundamental character pit, with the exception of the ability to guide arrows, and versatile recovery, it's all the players intuition, this coming from the fact that pit doesn't have me to guaranteed things in his favor.
The one thing I'm working on now is using turn around dairs the neutral.