SixSaw & 0RLy, be wary of CC when you go for Dair -> sour Uair. If CC'd, some characters can escape the follow-up even if it's a grab. I recommend this little string on floaties at low %'s, fastfallers after ~35%, and both only if the Dair hits. If it's shielded, abort unless they tend to sit in their shield after they shield your Dairs. I still wouldn't recommend going for a follow up after Dair is shielded though. You want to think of Dair like a vertical Shoulder Bash when shielded. They almost always have advantage and most characters have a simple OOS option that will beat or trade with just about anything Wario can drop on them. When my Dairs are shielded, I often use that moment to just DI well away for a brief moment and re-assess. Now that they have advantage, I step back and react to what they do.
The majority of Wario's combos are extremely DI sensitive, so I don't really have many bread and butter combos. I have a few strings that are my natural go-tos, but that's mostly how I am as a player anyways. I play almost 100% intuition, the rest I correct in baby steps.
A few little "things" I do often though...
Vs spacies on triple platforms, they always DI for the top plat. Usually, they'll shield if you jump up at them... bite. If they don't shield, well, just follow them with your aerial mobility. They're probably going for the other platforms. Usually if I get a spacie up top, I can do a lot with them.
Vs characters with slow OOS options, if they're standing at the ledge and you're coming up, LH instant Fair -> whatever. But if they shield, you poke with a falling Uair (very similar to the Dair -> sour Uair) or just Bite and throw 'em off.
Nair. All the time. Short hop it. All the time. Full hop it. All the time. Double jump with it. Bait with weave/fall with the sourspot -> dash JC grab. (My fav) Edgeguard with it. Vs spacies, Uthrow -> Nair regrab (My #2 fav, get **** on). Nair through shields and get behind and grab. Honestly, there is no move in this game more fun to spam than Nair. It's SO good.