Question  : What is the difference between Explorers of Hell and Explorers of Heaven?

Answer : Hell has modified dialogues, with a lot of dark humor, and Heaven keeps the same dialogues as the base game.

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Question : What is Pokemon Mystery Dungeon: Explorers of Hell and Heaven?

Answer : This is a hackrom of Pokemon Mystery Dungeon: Explorers of Sky. The game is much harder, there are new pokemon, 
dungeons, starters, items, and the dialogues are modified for Explorers of Hell. Beware, if you are not comfortable with dark humor, 
play Heaven.