spoilers but after you finish a regular run you need to go past oak and find his computer make sure you get mew from the code door upstairs at some point because it is impossible to beat mewtwo without it the code for mew is wish and you find it under a truck
I think it would be cool to make battle frontier have easy normal and hard mode easy is 30 battles normal 40 hard 50 you never get to battle against legendary pokemon (highest rarity) I would love to truely be challenged in this game I am addicted but I have got too good