If a pill hits, I'd say you don't have to do anything else for a while
But seriously, Pills are amazing, and if there's one thing Shroomed can do to improve his game, it's to use pills more effectively. If you watch him play against a fast character, you can see he has a hard time going in, and he doesn't use his pills very often (possibly because he feels like he can't).
There is an
extremely safe technique, however, that you never see anyone use: It's to dash away, hop (short or full) and turn-around B a pill: it puts a pill precisely where you were, and gets you outta there! So if your oppnent tries to rush you, they're going to have to deal with the pill. If you full-hopped, you can waveland away and toss out another pill, or grab the ledge and waveland back in for a counterattack.
Practice doing this out of a dash-dances or wavedashes, and you will be amazed at how mobile Doc (and Mario) will look.
Surprisingly, stages with platforms seem to magnify this technique's effectiveness. From my experience, there is very little your opponent can really do to counter the technique but throw out projectiles, which you can cape!
If your opponents start swatting away the pills, try wavedashing in with a well-spaced f-tilt to remind them you're capable of catching them off-guard.
Overall, use this technique to fluster your opponent and pressure them into an approach. At that point, you can do what Doc does best.
It's just one more thing that makes Doc so much fun to use.