Regen

Regen is an ability found in Kingdom Hearts: Chain of Memories, Kingdom Hearts Birth by Sleep, and Kingdom Hearts Re:coded. It automatically restores the player's HP a little at a time.

In Kingdom Hearts 358/2 Days, casting Cura has the same effect as Regen.

Mechanics
In Kingdom Hearts: Chain of Memories and Kingdom Hearts: Re:Chain of Memories, after the Oogie Boogie Enemy Card is activated, it restores health ten times before the effect runs out. When Sora's HP is in the alarm zone, Regen causes him to regain health more quickly.

In Kingdom Hearts Re:coded, Regen restores Data-Sora's HP every few seconds when he is wielding a Keychain that grants the ability at a certain clock level.

Kingdom Hearts: Chain of Memories

 * The Oogie Boogie Enemy Card has "Regen" as its ability.

Kingdom Hearts Birth by Sleep

 * Regen is a level 2 ability for the Cinderella Dimension Link.

Kingdom Hearts Re:coded

 * The Lady Luck ⑤ has Regen as one of its level 3 Clock Abilities.
 * The Oathkeeper and its upgrades have Regen as one of their level 2 Clock Abilities.
 * The Lionheart 3° and its upgrades have Regen as one of their level 3 Clock Abilities.
 * The Ultima Weapon 〉 and its upgrades have Regen as one of their level 3 Clock Abilities.

Etymology
Regen is derived from the word "regenerate", which refers to the health-regenerating attribute of the ability.