I usually never play with rotation mons/teams in a pokemon game and try keep some of my early favorites up until the very end, filling slots as I progress even if I don't have a team of six fully trained pkmn. I also don't care about EV/IVs. In a regular game it is manageable but for my first reborn run starting with e14 that was an unnecessary added difficulty (Kiki, Charlotte and Samson made me regret it). So I almost beat main reborn with a single team : Swampert, Ampharos, Arcanine, Roserade, Mismagius, and Eelektross. During the hiatus before the e19 beta I decided to train a lot of pokemon that were waiting and wasting their potential in my pc.
For the E4 I decided to switch 3 of my regulars for Dragonite, Gardevoir and Mimikyu.
Disguise and Trick Room were a huge game changer
Mega-Swampert and Dragonite with Multiscale were my MVP
Shoutout also to my stock of Revival Herbs and Max potions because without them that horrendous second battle would have been the end of me.