The extras' card, or rather the details cards are optional cards that don't come with the starter kit. These cards have to be made the player. The point is to write the long as descriptions of what certain techniques, skills, abilities, spells, and items can do without using up all the space you have in your inventory, treasure, and spell technique cards. The only rules here are that every description has to be approved by the dm and that the majority of the time these cards will be stored in the character's bag to save space.