I'm expending way too much effort trying to get a Pikachu on my Black 2.
You can't catch Pikachu at all in BW/BW2, which isn't a big problem because you can trade one up from DPPt/HGSS. However, the one I want is a Surfing Pikachu with Light Ball - legal in Gen IV, but impossible in BW/BW2.
I spent about 50,000 Pokéwalker steps trying to catch a Pikachu with Surf, only to discover that you can't trade up Pokémon that know HMs. Pikachu can't normally learn Surf, so you can't forget it and re-teach it on the other side.
Wild Pikachu sometimes have the Light Ball, but they can't be caught wild anywhere in BW/BW2, and you can't trade items from earlier generations either. You also can't acquire Light Ball anywhere in BW/BW2.
I don't want to just cheat, because then it won't be authentic. My plan is to take the Surfing Pikachu with Light Ball from my Gen IV cart, remove Surf and Light Ball, trade it up, and use a Pokemon editor tool to give it back Surf and Light Ball.