The O2 Machines are a little weird. The only way to obtain Oxygen from these things is by kissing them. They are only found underwater during Chapter 7 while you are trying to reach Tane Tane Island.
The machines look like Mermen, and are actually quite helpful. Get ready for a disturbing image if you use it though. They also have these huge lips, which are quite strange. After using them, all of the character's faces will be red. This can only mean one thing: He's kissing them. It is truly unknown how these "machines" can survive underwater, so it screams Homosexuality.
A land O2 machine is found in the Empire Porky Building. These ones have a horse as their lower half, similar to centaurs. They ask for one more breath for old times sake. Accept if you want.
 Game Appearances
These certain characters only appear in Mother 3. They appear in Chapter 7 as a major help, and in Chapter 8. Afterward, they don't appear until the Final Credits.