Invisible

Invisible, also known as Transparent, is a reoccurring status ailment that appears in the Paper Mario series.

Paper Mario
In Paper Mario, Invisible is a rather rare status condition. One of the only ways for Mario to become invisible is to use the Repel Gel which is rare itself in the game. Lady Bow's Outta Sight also functions as a one-turn Invisible. Gray Magikoopas can also use their magic to turn their own allies or themselves Invisible. When someone is Invisible, they are immune to all damage until it wears off.

Paper Mario: The Thousand-Year Door
Invisible returns in Paper Mario: The Thousand-Year Door where it's a little more common than from the previous game. This is because Invisible is now mainly caused by using a Boo's Sheet which can be bought in the Item Shop on the Excess Express. Certain other items such as Love Pudding and Kooky Cookie can cause the Invisible effect as well. Sometimes, a Boo may fly on the stage and turn either Mario, his partner, or one of the enemies Invisible rendering them unable to take damage.