In my group I had to come up with the card designs and all the mechanics that go with them. I started with a few idea's and play tested each to see how they would actually work with our board game. This required a few different session to get a final idea on how the final game would work.
the final idea worked using a different set of cards with separate illustrations and comments demonstrating what each of the different cards worked, these were only used in combat against other monster such as the junk titan. Their were also environmental cards which did not work as well as intended as it got difficult to track when it had been 5 turns and events cards which could either help or hinder the player depending what card was chosen.