A P-Acorn is a item in New Super Mario Bros. U. It transforms its user into Power Squirrel Mario with the ability to fly an unlimited number of times for the entire stage, similar to the P-Wing from previous games. In Mario's case, his hat and shirt becomes white; his hat has a large, red "P" instead of his "M" emblem; and he also appears to have a sheen around him. The P-Acorns power will perish if the player completes a level without losing the power-up, causing the player to change back to the regular flying squirrel form. However, the player will not lose the power-up if the course is completed via capturing Nabbit.
To obtain a P-Acorn, the player must either capture a Nabbit and return its sack to a Toad, or after defeating Bowser, if the player saves their profile then opens it again, a P-Acorn will appear instead of a Super Acorn (it also seems to appear at other times). Its appearance is similar to the Super Acorn, but has pale white and gray stripes on the top, scarlet bottom, and it has a large, red "P" imprinted on the top.
It should also be noted that the player is not able to make a Miiverse post if a level is completed with this power-up, even if the level is cleared without taking any damage. This is the same way if the level is completed while playing as Nabbit in New Super Luigi U.
The sound effect heard when flying through the air in the this form is the same one heard when flying as Raccoon Mario.
Names in other languages