- "Buuurp! So you are Ness? ...I see... Gyork! Gyork! Gyork! There's a prophecy that a boy will destroy Master Giygas. Heeg! Heeg! Heeg! You make me laugh so hard... If Master Giygas is scared of someone... he would have to be worse than the greatest evil... Garg! Ga! Garg! Ga! Ga! Ga! I'll take you down big time, so get ready for the worst fight of your life! Gha Gha Gha! Get ready to feel the pain of true nausea! Ghe Ghe! Come on, let's go!"
- — Master Belch
Master Belch (Geppu-sama), later called Master Barf, is a boss in EarthBound that is fought twice. He is a large, animated pile of vomit who is one of Giygas's most esteemed minions. He is addicted to Fly Honey and is in command of many smaller piles of vomit. Belch enslaves the Mr. Saturn at one point to mass produce Fly Honey. He can be distracted by the Jar of Fly Honey when the party confronts him in his factory.
Master Belch reappears in the Deep Darkness as Master Barf, and attacks the party. This time, he is immune to Fly Honey if the party happens to be still carrying it. After he suffers enough damage, Poo returns from his training with the Star Master and kills Barf with his newly learned PSI Starstorm ability.
As his names imply, he belches repeatedly while speaking, and this sound even appears in his battle theme (called "Battle Against Belch"). Curiously, in Master Belch's clay model, he is blue despite the fact that none his forms depict him as such.
There is actually a way you can defeat Master Belch without the Fly Honey, though you must have the luck to do so. Generally, at the beginning of every run-in with him, he'll blow his nauseating breath at you. If you use PK Flash and get the 1/8 to make him feel strange, he'll blow his breath, making him feel nauseous. The main reason why you usually need the Fly Honey is that before you use it, any attack on him will auto-heal him, but this doesn't apply to status ailments. If you manage to deal 650 damage to him via nauseousness, he'll go down.
- He also appears in Magicant as one of Ness' memories. If talked to him, he will say "You have destroyed my pride, Auuuuuuugh!" and the background will change to a purple and dark tone.
- It is possible to defeat Master Belch without Fly Honey the first time you encounter, but it is very difficult, since the damage taken to Master Belch gets fully recovered every turn.
- Belch's in-game sprite does not match his clay model represented on the back of the box. Belch's in-game sprite is Green (later Pink), while his Clay model on the back of the box is Blue, which matches his beta Blue Sprite as seen in early footage of Mother 2 (the Japanese version of Earthbound.) It is unknown why the change was made between versions, but this error seemed to have been carried over to Earthbound (or at least was planned to due to the back of the U.S. box portryaing this version of him.)
- Although his second form is called "Master Barf" he says that he "changed his name to Puke".
- Master Belch appears as a neutral class primary spirit in the new Spirits mode in Super Smash Bros. Ultimate. Despite having an official clay model, his battle sprite is used instead.
- In Super Mario Maker, there is a Master Belch costume that can be unlocked by completing an event course titled, "Master Belch's Base". By pressing up on the d-pad, you can make Master Belch burp.
- Belch's name is a onomatopoeia of burping. His Japanese name Geppu (ゲップー), is a Japanese onomatopoeia of burping.