Friend cards appear in Kingdom Hearts Chain of Memories as a type of playing card which summons an ally of Sora or Riku to help them during battle. They can be identified by their green borders, which they share with item cards. Friend cards behave identically to the other types of playing card, but unlike the others they cannot be collected, and are instead randomly obtained during battle and disappear when the battle is finished.
As in Kingdom Hearts, these allies generally cannot be used on all worlds. Each friend summon can be upgraded to more powerful levels by stocking multiples of that friend card, though they can also be used in various combinations with other friend cards, as well as attack, magic, summon, and item cards to perform different spells and summons unavailable in the other games. Many of these new combinations are Kingdom Hearts versions of traditional Final Fantasy spells like "Terror" or "Teleport".
Friend cards are available in both Sora's tale and Reverse/Rebirth, but are only used by Sora and Riku.
List of friend cards
The Gimmick Card, also known as the Trick Card, is a special Friend Card that can be obtained under certain conditions during boss battles. It depicts a green Hidden Mickey. The card acts as a 0 card, but cannot be broken and will still take effect if used against another 0 card. Using a Gimmick Card will generate effects that can give Sora and Riku the upper hand. In practice it is quite similar to a Reaction Command.