Board Thread:General Discussion/@comment-17694930-20140301174515/@comment-66.62.115.199-20140301192706

As far as I know, the only way to control which card is selected to assist others are the ones listed as your Favorite, recently been your favorite, or is in one of your attack units.

If you pay attention closely, you can tell what cards from your comrades are coming to assist you (often times it's the same or similar cards over and over again).

Sorry if I'm incorrect, but this is just what I've gathered from experience and what others have said.