Big Mouth appears as a giant green head with an exceedingly large mouth. It has eyebrows, two angry eyes, and purple cheeks, all above its giant mouth. Big Mouth's giant mouth has a design of a human mouth, having a design of a human mouth and twelve teeth.
Big Mouth rotates clockwise in the level, staying in the same place at all times. To pass the level, the player has to enter his giant mouth from the left side of the level, and stay in it until there is an opening on the right side. Touching any part of this mouth will hurt the player.
Big Mouth Jr.
Big Mouth Junior is what seems to be a younger version of the big mouth enemies seen in Hot Air 2. Big Mouth Junior appears in only one level of Hot Air 1, on level 12.
Big Mouth Junior has the same appearance as big mouth, but considerably shrunken. Big Mouth Junior has a giant mouth cut out of it, but incredibly smaller than big mouth's, and has four teeth instead of big mouth's twelve. Jr's purple cheeks are locate on the side of its mouth instead of close to the eyes.
Big Mouth Junior acts exactly like Big Mouth in Hot Air, only Jr. moves slower, as well as has a smaller mouth. In the level it appears in, in Hot Air 1, there are three Big Mouth Jr's. For the level to be completed, the player has to only go through two.
To complete the entire game, the balloon has to go spend more time in each mouth, go through four instead of two (going through one mouth twice), and risk getting itself popped. The level Big Mouth Jr.'s appear on is made difficult due to the very small mouths, where the player has to spend a long time in as well as move correctly, lest they get popped.