From the Super Mario Wiki
The Superguard is a move used in Paper Mario: The Thousand-Year Door. It is a more advanced version of a Guard. It stops any attack from doing any damage at all, and any direct-contact moves will be returned to the attacker, causing the enemy one Heart Point of damage. This counterattack damage does not stack with other counterattack effects such as being electrified. On indirect-attacks, the Superguard will simply negate all damage, with the exception of a Pokey's body segment throw attack, which will send the body segment back to the Pokey and cause the same amount of damage the attack would've done to Mario or his partner. It will also block any status effects from an enemy attack. X-Yux's immobilizing ability can only be blocked by a Superguard. The counter-attack effect of the Superguard does not work on the Armored Harriers. Neither Mario nor the Iron Cleft that hit him will take any damage, presumably to force the player to acquire Yoshi to defeat them. There are also only two attacks in the game for which the Superguard will not prevent all damage: Bonetail's bite attack and an explosion from either a Bulky Bob-omb or a Bob-ulk.
Despite being incredibly useful, it is even harder to execute than a Guard, requiring a press of 3/60 of a second before contact compared to a Guard's requiring a press of 8/60 of a second before contact.. If done correctly, Mario or his partner will spin around and words will pop out next to them saying "GREAT" in orange, compared to just guarding, Mario or his partner will just retain a ducked position, and the words say "NICE" in blue.
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