Wario and Sonic for example, you have to wall out w/ your aerials a lot, even to the point of it being counter-intuitive at times, because it's much harder for them to get inside or to punish your whiffs if done properly. Marth, you want to stay planted on the ground at almost all times. Ground games like D3/Snake you have to do a lot of cross up work and make them guess where you're going to be, and using frame 1 FP is really good on them for this reason, since their biggest option is shield naturally.
v. Fox, I actually have to say Steam that a good tactic to mix in is a lot of full hop or really long distance baiting with laggy looking moves. Foxes are usually used to getting to punish everything, you can often make them commit to predictable/laggy stuff (most ones that don't use fox consistently anyways, good dedicated fox mains sometimes know better and will do more creative punishes like nair or whatnot). If you can do that with your close cross up game, you can keep him really guessing on what's punishable and what isn't (although he's going to stuff you a lot up close too).