"Killer" Dungeons part 1

Dungeons that are hard for the players to the point of generally having a high character mortality rate have one or more of the following characteristics:

• Challenge ratings or the equivalent are ignored.  A wrong turn or sometimes just a turn leads to an encounter that is not really meant for the level that the characters are at, such as 4th level characters stumbling onto a hill giant.
• Lots of encounters are in close proximity, making healing between fights difficult
• Most of the fights are only winnable if the characters are at full strength and willing to use all their full arsenal (such as daily powers or high level spells)
• In earlier editions...timing events where if the characters do not say "I run away" within 10 real-time seconds, the characters are crushed by a mechanical block trap
• Somewhere in the dungeon is a slippery high spot that has a long drop associated with it.  (ie a lethal fall off a cliff)
• In earlier editions...save or die effects from monsters and traps.  Characters that have to make 5 or more of these rolls in a given dungeon are bound to miss one.
• Pregenerated player characters for use with the dungeon are malformed and never would have made it to 8th level with only 30 hp as a fighter except as a module character
• In a related note, pregenerated characters make odd spell and equipment choices, making it unclear how the character survived so long
• A couple of traps early in the dungeon to get the characters if they are not paying attention.  Then no traps through the middle, then after several hours when the players have forgotten to start searching for traps again, several lethal traps near the end of the dungeon.
• A mixture of friendly and neutral monsters thrown in so the characters cannot just obliterate everything that moves.  Characters can pull off some fairly deadly ambushes if they know that all of the monsters are evil.
• Misaligned treasure.  Weak monsters have really good treasure.  Tough monsters have really poor treasure.  This disorients the players and distracts them from safely navigating through the dungeon.
• Obscure monsters are better than common ones.  They tend to be slightly nastier and scarier.
• Monsters using special abilities intelligently, generally to force the characters into natural hazards or off edges of cliffs
• Have one or two really unsafe areas.  There is always a character who has to test firsthand whether the stuff that obviously looks like lava on level 10 is really lava or just warm red water.

That's all for now.  More thoughts about "killer" dungeons in a later post...