Guard
Guard is a defensive move used in Paper Mario and Paper Mario: The Thousand-Year Door. It is used to reduce damage dealt by enemies. By pressing 
just before contact, damage can be reduced by 1; the player has only 8/60 of a second[1] before the attack connects to press the button. Guarding will also negate almost every Status Effect linked to the attack, such as Poison (the only exception is immobilization, which only one enemy in the series can perform without an item). If equipped with the Badge Damage Dodge, Guards can prevent additional points of damage. Simplifier and Unsimplifier badges will loosen or tighten the window to Guard. Guarding reduces damage even against piercing attacks.
Should an attack target both Mario and his partner, the player only has to successfully Guard the first hit; whoever gets hit second will automatically take whatever defensive action (Guard, Superguard, or neither) the first did. Because of this, there is a bug where the player cannot control what the second target does if the attack misses the first target - the second target's action will match whatever the last defensive action was for the previous attack.
The Guard is the weaker version of the Superguard, which will block all damage and status effects along with a small counterattack, yet requires tighter timing.
