After a bunch of underground catching and thinking, I got what seems to be the team for Piplup.
Before Gardenia, I went into the underground and caught Togepi, Misdreavus, Croagunk, and Chingling(aboveground).
The team during the battle became:
Prinplup, Togepi, Misdreavus, Croagunk, and still Chingling. I wanted to run around in circles for like an hour to get enough happiness to evolve and all that stuff, but I didn't find it worth my time. I was able to actually take down Gardenia first try using some charm and yawn strats(really? they made Roserade mostly physical?). Only 2 of my mons fainted, with them being Misdreavus and Togepi, I believe. Could've stopped Togepi from fainting, but it is what it is. Probably could've had no faints if I thought about it more, but I had fun. That was my first time fighting Gardenia with anything other than a coked-up Monferno rolling around with Flame Wheel, so it was nice to have to think.
I caught as many underground mons as I can to get acceptable IVs (and egg moves since the underground gives those) on my team.
My final Piplup team's gonna be:
Empoleon, Togekiss, Mismagius, Toxicroak, Chimecho(I guess? lul), and Mamoswine.
I think I have enough speed so I'll hold off on using Weavile, because that's what I took with me on my 2nd Chimchar run. I've already used Mamoswine before I got Sneasel on that run so I might get Abomasnow if I don't care about hail damage.
Decided to take the tryhard route and grind a Ralts up to lv 30 so it's a Gardevoir, who gets Wish at lv 28. When I get to Pastoria City, I can relearn Wish and then breed Male Garde with my female Chimecho so it has Wish. I'll have 1 cleric and then I can make the eventual Togekiss learn Wish at a later level in case I need it. I kinda really like my team as it is right now, so I may not do it... But I already grinded that Ralts to lv 30 so I might have to so I don't tell myself that I wasted an hour throwing leaves at Gastrodons. Having a blast though.