Deep and Evil
In MOTHER 2, the jungle area is called the “makyou”, which is a word that’s difficult to translate into English. If pushed to give a translation, something like “evil lands” might work I guess. I’ve seen some MOTHER 2 guides call it the “Evil Zone”, in fact. It’s a very ominous name in Japanese, but sounds kinda meh in English.
It truly is a tough word to translate (not to mention make it sound good), so in EarthBound the name was changed to “Deep Darkness”. I feel this is a really good translation that maybe even surpasses the original; it’s unique AND emphasizes the “not being able to see anything” aspect of the place.
To Belch or to Puke
In EarthBound, when you encounter Master Belch again in Deep Darkness, he tells you that his name has changed to “Puke”. But when you fight him in battle, his name is shown as “Master Barf”.
In MOTHER 2, he says his name has changed, but he doesn’t say what it is. Then, when you fight him, you see his name is “Return of Belch”.
Basically, the names “Master Puke” and “Master Barf” were made up for EarthBound and used inconsistently, and his text was slightly altered to make mention of this stuff as well.
While Master Puke is talking in EarthBound, he says, “Peeeeyouuu!” It always seemed weird to me that he, a pile of stinky slop, would be offended by his smell.
It turns out that in MOTHER 2, that line is actually the Japanese onomatopoeia for breathing stinky breath onto someone. So he’s actually breathing his stench-filled breath onto Ness and the others.
After you beat Master Puke in EarthBound, you’ll always win the Casey Bat. This is a reference to the old poem Casey at the Bat, and as you might expect after reading the poem, the bat is strong but misses enemies most of the time.
In MOTHER 2, this bat doesn’t have any connection with Casey or anything else. It’s called something that’s tough to translate well, but is something like the “Swing with All Your Might Bat”.
Since that’s a real mouthful to say and since it’s too long of a name, the localizers probably had to trim it down and/or call it something completely different, and the Casey poem happened to be an absolutely perfect fit for it.
This is definitely a case where I think the localization is greatly improved over the original.