In my opinion, the super Battle Subway may be even harder than the Battle Tower of Gen 3/4, although I think I had a worse team in this game. Even legendaries appear as you get to the end.

You will be going up against mostly fully evolved Pokemon. You need to beat 49 battles in a row without losing once to reach the Subway Masters. However, then you unlock the Super Battle Subway where the real challenge starts.

The normal Battle Subway is a cakewalk, just beat 21 battles with unevolved Pokemon in a row. For whatever reason I expected it to be way easier than the Battle Frontier of Emerald / Platinum but I was very mistaken. The second major roadblock is the Battle Subway. However, if you have caught them all in Gen 3/4 you should be prepared for this generation. There are some really annoying 5% rustling grass / whirlpool / whirlpool fishing encounters (Lapras and Politoed have Perish Song) so it may be worth saving your master ball for those instead. I recommend using your master ball on Tornadus or Kyurem based on whether you want to deal with catching a roaming legendary legit. For whatever reason, you only need 201 national dex Pokemon for this set. There are 130 regional dex and 202 national dex Pokemon to catch. The first major roadblock to mastering this set is catching them all. It is still quite difficult, probably surpassing every main series Gen 1,2,3 except possibly Emerald version. This set was a breath of fresh air compared to the horrors of the Platinum version set. Mastered! According to RetroArch, this took me 53:11:53 in real time (mostly sped up) and I finished with a final In-Game time of 67:15.

Pokemon black version 2 nintendo ds