Leech is an additional effect to certain attacks in Sonic Chronicles: The Dark Brotherhood. It can be inflicted on both playable characters and enemies by using certain attacks, such as POW moves or regular attacks (enemies only).
When an attacker manages to succesfully damage a target with Leech attacks, the attack will regain a certain amount of his/hers own Health Points. In gameplay, when the Leech effect is being used by a character, there will appear a green number above the spot on the battlefield where the user of the Leech attack stands at the same time when the orange number displaying the damage that the target received from the Leech attack appears. The size of the green number tells how many Health Points the user of the Leech attack regains. If the user of the attack cannot regain any more Health Points that they already have, the green number will simply display 0.