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Guard is a defensive move used in Paper Mario, Paper Mario: The Thousand-Year Door, Paper Mario: Sticker Star and Paper Mario: Color Splash (under the name Block for the two latter games). 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 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. Two Simplifier badges or one Unsimplifier badge will respectively loosen or tighten the window to Guard by 1/60 of a second. 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.
In Paper Mario: The Thousand-Year Door, there exists a much stronger version of this move, called the Superguard, which will block all damage and status effects along with a small counterattack, yet requires tighter timing.
Mario & Luigi: Paper Jam, Mario & Luigi: Superstar Saga + Bowser's Minions and Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey have a defensive move called Emergency Block and Emergency Guard, respectively, which players can use by pressing and holding (in Mario & Luigi: Paper Jam and Mario & Luigi: Superstar Saga + Bowser's Minions) or (in Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey) if they are having trouble avoiding damage in a particular situation. Like in the Paper Mario games, the Emergency Block/Guard can reduce damage taken by Mario, Luigi and Paper Mario (in Mario & Luigi: Paper Jam). However, it does not prevent Status Effects.