The dsiware downgrade would involve you having a friend with a pre-hacked console. You'd also have to buy a $5 game on their hacked console. You'll also need a hax entrypoint. I don't understand what you mean by 2ds games though. Do you want to play games such as Pokemon Soul Silver, which were released for the old consoles like the Ds, and Dsi? Or do you want to play newer games like Pokemon Y which were released for the 3ds? You can buy a $10 flashcart and play all of the old Ds games you want on it.