The Impair Psynergy series is a series of two Mars based Support Psynergies found in both Golden Sun games that are used to lower the Defense of one or more enemies. This series is available to both of the default class series for the two Mars Adepts, Jenna and Garet, the Flame User and Guard respectively. It is also available to the Brute class series, as long as the class is at Savage or higher, allowing the Venus Adepts Isaac and Felix to learn the series as well.
Impair is available to the Guard and Savage at level 9 while Flame User learns it at level 10. It costs 4 PP and is used to drop the Defense of 1 enemy by 25%, and can be used again to lower it to 50%. The manual to the North American version of The Lost Age, in one instance, incorrectly refers to this Psynergy as "Weaken", which is a different Psynergy of the Jupiter element that lowers Resistance.
Debilitate is available to the Savage and Flame User at level 23 while the Guard must wait until level 26. It costs 6 PP and is used to drop the Defense of up to three enemies by 12.5% and can be used repeatedly, up until 50%.
This is a fairly staple move within the RPG genre, lowering an opponents defence can be a valuable asset to the player's offence, especially since it does work on most bosses. However, it only lasts for a short period of time, meaning that to make it useful, the increase in damage dealt before it wears off must exceed the damage that could be done through attacking normally. Due to the high attack and low PP of the Brute and Guard series, it may be more efficient to simply attack or use a damaging Psynergy. Because of this, while it won't be used all the time, it remains situationally useful.