Each Pokemon card has a list of the monster's strengths, weaknesses, hit points, level of evolution, and retreat costs. In order to attack another Pokemon, the player has to use the energy shown on his own Pokemon card, and that energy has to be activated by an energy card. If an opponent's Pokemon inflicts more damage than a Pokemon has hit points, then that Pokemon is knocked unconscious and is out of the game. No player may have more than six Pokemon cards on the field at any one time.
Energy cards allow the Pokemon cards to attack and activate other special effects. "Basic Energy" card types include darkness, fighting, fire, grass, lightning, psychic, water and steel. "Special Energy" cards provide additional effects and can add power to a Pokemon's abilities.
Trainer cards represent a Pokemon's human trainers and game allies. They can bring a knocked-out Pokemon back onto the field or remove energy from an opponent's Pokemon. Trainer cards are broken into several subtypes, including pokemon tools (which can be attached to Pokemon cards and provide a specific benefit to the card), stadium cards (which provide specific effects for both players), and supporter cards (which allow the player to change his deck in specific ways).
Certain cards acts as more than one type. For example, there may be a Pokemon made of electricity or some other energy, allowing it to function as both a Pokemon card and an Energy card. These multi-type cards list their specific functions in their rules text.
The Pokemon game contains thousands of different individual card types, and some of them are considered too powerful for formal play. The list changes with each new Pokemon set released, though Pokemon's publishers, Wizards of the Coast, do try to keep banned cards to a minimum. These cards must be removed from any deck played in an officially sanctioned Pokemon tournament.