It's kinda hard. Your Pokemon are all set to level 50 even if they're above it, and your opponents have level 50 pokemon too. You have to beat 7 opponents straight to win a round, and at the end of the third round your 7th opponent is the "Frontier Brain"
Which is this dude, and he totally hax. He has Dragonite, Milotic (a water thing) and Rhyperior (evolves from Rhydon ._. wtfz)
And yeah, MAJOR HAX. I used Lanturn, Tyranitar, and Sandslash (1st/2nd gen only ftw) to beat him. All I had left was Sandslash, with 5hp. lol.
It's frustrating losing to him though, because then you have to win 20 straight battles again, and some of your opponents are complete wastes of time (like, they'll use stuff like Pichu) and others will randomly destroy my team because they got lucky and have the total counters.
I like 6 Pokeman battles better than 3, for this reason. :\