Trulon: The Shadow Engine (EP)

Random battles are the ones that take place on the world map. You will get a notification that you found something and need to investigate. Sometimes it will only be a chest and experience orb, but often it is a group of enemies. There are X different cards in the game, and you are guaranteed to get a different one each time you win a random battle, so complete X of these encounters to unlock the achievement. This will easily come as you grind to Level 30.