The Malevolent Ultimate Dungeon of Doom

From the introduction: So...your players think the Temple of Elemental Evil was a joke. Tomb of Horrors? Walk in the park. They cleaned out the lower levels of Hell in one afternoon and the ranger wears Tiamat's head as a helmet. How can you challenge them? Ladies and gentlemen, I present THE MALELOVENT ULTIMATE DUNGEON OF DOOM, or MUDD for short.