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|Number of Levels||18 normal,2 world boss level|
|World Boss||Legion, The Abomination|
This world is unique in that it is a point of no return. You cannot return to past worlds once reaching here. This world lacks save points. Instead, you are given the opportunity to save after beating specific levels.
If the player does not meet certain conditions, the game will conclude at The Castle of Meat.
- World 0-1: The Gate
- World 0-2: Gravity Well
- World 0-3: Ocean of Souls
- World 0-4: Hall of Mirrors
- World 0-5: Miasma City
- World 0-6: Melting Room
- World 0-7: The Great Maze
- World 0-WB: The Castle of Meat
After clearing World 0-8 and meeting certain conditions, the game will continue into these levels. These levels are the most unique in the game in that you are forced to use certain characters for these levels.
- World 0-10: The Abyss
- World 0-11: Speedway of Screams (Sonic's nightmare level)
- World 0-12: Red Arremer Heaven (Arthur's nightmare level)
- World 0-13: Hall of Forgotten Legends (Link's nightmare level)
- World 0-14: Banquet of Decay (Kirby's nightmare level)
- World 0-15: Megaman Museum (Roll's nightmare level)
- World 0-16: Greed Trap (Wario's nightmare level)
- World 0-17: Nightmare Hill (Tails' nightmare level)
- World 0-18: Paradox Zone (Samus' nightmare level)
- World 0-19: Lonely Rock (Luigi's nightmare level)
- World 0-20: The Dying Twilight (Mario's nightmare level)
- World 0-WB2: The Castle That Doesn't Make Sense
|Worlds in Mushroom Kingdom Fusion|
|World 1 | World 2 | World 3 | World 4 | World 5 | World 6 | World 7 | World 8 | World 9 | World 0 | World -1|