flashcards are bad for online play because .3ds/.3dz roms require "headers" whereas installed .cia files have no requirement. You can play online with cia installed games without ban risk (unless cheating.) There are a few other risks, like do not cheat with the "Badge Arcade" game, maybe other risks but those are the 2 to avoid: playing with flashcards (just use .cia roms installed to the SD) and cheating at the Badge Arcade.