Reserving for Mandibuzz, a Budew.
Take Eigen, the Budew. Or actually, Eigen the army of Budews. See, catching one Budew is stupid, it's More likely than not to have crap IVs. So you caught a bunch of them. And you'll keep catching more as you need them.
The thing is, each Budew (Eigen1, Eigen2 and so on) isn't too happy that it has to compete with other Budews for your love. So, each one wants to be unique and make itself as special as possible. To do this, each of your Budews that you catch must have one TM taught to it. Also, choose TWO moves in Budew's moves, and those two moves all your Budews may have. The last move must be unique to each Budew (so that's two shared moves, one TM move and one unique level up move).
First, use one of the Eigens to solo Wake, as a Budew. There is no need to solo the gym trainers as well, but you can if you want.
After that, the other Eigens get jealous, thinking you like this Eigen more than you like them. So they decide to team up. With a party of two Eigens, you must solo one of the battles against a Galactic Admin (Mars, Jupiter, etc).
Then other Eigens get even more jealous, and so with a team of three other Eigens (and only those Eigens, the other slots should be empty), you must solo the Distortion World in its entirety (you may evolve these Eigens beforehand if you deem it necessary).
Finally, the first Eigen gets annoyed that others are stealing it's spotlight and have even evolved. So it's got to smash through Sunyshore Gym (trainers and leader) by itself, and it must have evolved before the battle.
Finally, solo the entirety of Victory Road with a team of all your Eigens (you should have six by now).
By now, they've reconciled, so they decide that frankly since you've shown no love for them at all, they'll show you no love either. They take away all your items just as you entire the E4's chambers, and refuse to even be in your party. Thus, you have to beat the E4 with your other five Pokemon and with NO ITEMS. And you must do it in such a way that you end up using Struggle on your Pokemon to beat 3 of the Champion's Pokemon. You can use however many Pokemon you want, but they must use only Struggle to beat three of the Champion's Pokemon.