I define broken cards as cards which have no Digivolution Requirements that can be met. If no Digivolution Requirements can be met then it can't be used in game so is broken by design.
There were originally a lot more cards in this list before I added the French Mega Pack and the French Booster Set 3 to the site. But now the only cards that can't be used are from American promo sets that clearly had no regard for the game itself.
I still don't like the fact that some cards can't be used without mixing French cards into your deck, but complaining about how poorly Digi-Battle was managed is more than a bit of a lost cause at this point.