Showstopper

Showstopper is a special attack in Paper Mario: The Thousand-Year Door. Unlike most attacks which deal a certain amount of HP, this attack applies the "Instant KO" status effect, which has a random chance of immediately defeating each enemy in the battle. It is learned when Mario obtains the Garnet Star in Poshley Sanctum at the end of Chapter 6. The Action Command requires the player to press a random sequence of buttons that appear on the screen, in the order they appear. Getting the whole sequence correctly brings up another sequence with one additional button, up to a total of 5 sets of buttons. Once a player completes all five sequences, or they make a single error, they will stop and the attack will commence, its chance of success dictated by the number of sequences the player completed. This move uses 2 SP.

As a status effect-inflicting attack, every enemy has a different rate of success of being affected, which is then modified by the success of the action command. In general, weak enemies such as Goombas are easy to defeat with the move even when the action command is not perfect (having a success rate of 150%), while stronger enemies (especially those in the deeper floors of the Pit of 100 Trials) have success rates that vary between 80% and 20%, while the majority of bosses and minibosses cannot be affected at all - the main exceptions being all but the final boss of the Palace of Shadow, each one having a success rate of either 5% or 1%. Crazee Dayzees and Boos (and their variants) also have a very strong resistance to the effect.

Trivia
Despite normally not being able to obtain the Showstopper until the end of Chapter 6, the second form of Doopliss (the one fought on Twilight Trail and the Creepy Steeple rematch) has a 3% chance to get KOed by Showstopper. All other bosses fought before obtaining Showstopper are immune to the attack.