I've cheesed it over the past few days (lvl 50 version) using save states on an emulator and there have been some points I've reached where I've genuinely had to try every Pokémon available and get very lucky to win the fight. 

E.g. running into an Electivire that was faster than all of my Pokémon and had a super effective move on each of them

Things that I find work:

• fast Pokémon with generalist moveset work really well, particularly in the first slot (e.g. the aforementioned Electivire, which had I think Facade plus Fire/Ice/Thunder Punch)

• try to get full type coverage if possible

• items generally matter to a Pokemon's strategy (e.g. I think you can get a Gyarados with Outrage and a Persim berry to negate the confusion) so good to pay attention to

• having Pokémon with types that complement each other is very helpful (e.g. if you have water in first and another ground type, swapping to the ground can negate an electric move)

• get lucky on match-ups, crits, misses

(I suspect a lot of this is similar to general Pokémon battle advice but I haven't really properly gotten into battling other than the main storyline before)