Have a Pokemon that have moves that can hit multiple Pokemon at once (e.g. Dazzling Gleam, Surf, and Earthquake.) You should also have a Mimikyu on your team, courtesy of Disguise, or have Rest and Chesto Berry, Protect, Detect, etc. Also, go to the moveset checker to see what Pokemon have the most coverage. Since I already calculated that, the answer would be Electric, Ice, Ground, and Fighting. Mega Kangaskhan (Post Game Only), Electivire, Kangaskhan, Gengar, and Chansey (in order in most to least recommended) can learn these typed moves. Hope I helped!
Have a Kangaskhan with either its Mega Stone or a berry with Earthquake, and attacking Electric, Fighting, and Ice moves that can hit multiple Pokemon if possible.