>>32241192If you get Mareep in the ONE chance you have to get it. BW2 are challenging mainly because of the luck factor in getting good stuff early on, especially if you picked Tepig. Pray you get a good Water or Grass type or you're basically fucked, and this has happened to me. It's alright once you've passed Clay (until the brutal lategame), but that is the deciding point.
Platinum is hard basically because bosses are hard, and it's really mean early on. It's easy to have a lot of deaths early.
Sun and Moon can be pretty balls to the wall as well - not just the totems, but a lot of bosses have 31 IVs across the board and EV trained mons as well. You practically need Exp Share on in some places as well because grinding is nearly impossible. Especially from Poni Island onwards as the levels jump drastically.