There are nine types of energy cards, including grass, fire, water, lightning, psychic, fighting, darkness, metal and colorless. Each Pokemon must use a certain type of energy card in order to attack or use his special abilities. For example, Pikachu is a lightning-type Pokemon and requires lightning energy cards to use most of his attacks. The exception are colorless Pokemon, which can use any type of energy card to attack and use their special abilities. Note that you are only allowed to attach one energy card to a single Pokemon per turn.
Energy cards in "Pokemon: The Trading Card Game" allow your Pokemon to attack, retreat and use their special abilities. Energy cards are played by attaching them to your Pokemon cards. Without energy cards, it would be almost impossible to win, because your Pokemon would not be able to complete any actions. Because of this, effective Pokemon decks have more energy cards than any other type of card.
Attacking and Abilities
Energy cards allow Pokemon to attack and use their special abilities. Many Pokemon have at least one attack and one special ability. A Pokemon's stronger attacks and abilities tend to require more energy cards than weak attacks. For example, Kabutops can use his "Sharp Sickle" attack if he has two fighting-type energy cards attached. His more powerful "Absorb" ability requires four fighting-type energy cards. Note that any energy card can be used for attacks that use colorless energy.
The types of energy cards a Pokemon uses determines if he can deal extra damage to a Pokemon who is weak against a particular type. For example, a Pokemon who uses water-type energy cards to attack deals twice as much damage against Pokemon who are weak against water. A Pokemon's weakness is shown on the bottom left side of the card. Note that there are no Pokemon who are weak against attacks that require colorless energy.
Energy cards are used to let your Pokemon retreat from battle. This is done by removing the required number of energy cards from the Pokemon who is retreating. Each Pokemon has a retreat cost that usually correlates with how powerful a Pokemon is. Stronger Pokemon usually have a higher retreat cost than weak Pokemon. All retreat costs are colorless, which means that you can discard any type of energy card to let your Pokemon retreat.