In return for letting it snow in Southtown, Heat Miser demands that he be allowed a day of warm weather at the North Pole. Didn't spending a day in Southtown cause Vixen to become terribly ill? Now all of Santa's reindeer are going to be exposed to that climate.
Another bit of Fridge Horror that's more of a Fridge Tear Jerker is this notable difference between the Miser Brothers' songs. Snow Miser's song goes "Friends call me Snow Miser", while Heat Miser's equivalent lyric is "They call me Heat Miser" Is a Green Christmas so unpopular that Heat Miser doesn't have any friends? That's kind of sad. No wonder he's always angry at his brother.
Possibly supported by the fact that he accuses Snow Miser of being Mother Nature's favorite.
"Whatever I touch, turns to snow/starts to melt in my clutch." Yeah....that is pretty much the epitome of fridge horror.
To be fair, though, Snow Miser can change the stuff he turns into snow back to its original form (he even demonstrates this) and we can assume the same is true of his brother. Plus, they're both Large Hams, so they might have just embellished this a bit.
The original 1974 special had Snow Miser and Heat Miser explicitly say that they are step-brothers, but the spinoff/sequel "A Miser Brothers Christmas" shows a flashback that depicts them as being fraternal twins since infancy. This may seem like a continuity error, but when you remember that the Miser Brothers hated each other, it becomes possible that the Miser Brothers simply hated each other so much that they pretend that they are not really related. Such a thing is not unheard of in real life cases of sibling rivalry.
When Santa becomes sick and decides not to deliver presents this year because of a lack of Christmas cheer, multiple papers report on the story. Despite this, apparently none of the children seem to care that Santa is sick because they're too old to believe in Santa.
When Jingle and Jangle visit the mayor to try and get Vixen out of the city pound, the mayor doesn't believe in elves, Santa, that their dog is a reindeer, or anything else Jingle and Jangle tell him. He does agree to believe them if they make it snow in Southtown, only doing so because he believes it is impossible. Immediately after, he goes outside and tells everyone that it is going to snow and there will be a white Christmas.