Board Thread:Question and Answer/@comment-129.100.253.82-20161206203228/@comment-29474392-20161206225152

Unfortunately you can only use a card once in attack units. You can use those same cards in Elemental Hall Units and also in Thor Units.

I don't know why not. I would be useful if your team for FAW is slightly different to your LAW team, yet you'd like to use some of the same cards. I'd love a 4th attack slot too, so if you wanted you could have attack teams in all 4 elements.