Dungeon encounters/traps.

[Aries1918]

Random mimic attacks would be awesome.

That'll make rogues take bodyguards with them

[Peridan]

We tend to do that anyway.

[Dave Fritz]

*declares self-interest*

As a rogue-type character, I'd be in favour of XP for traps and locks.

[roguethree]

Also, rooms/really good loot containers that require serious search/spot (whichever it is) and open lock skillz to find and access.

Some of these doors are circumventable by bashing them down, but doing so draws the attention of vicious, ruin your day wandering monsters like rust monsters and basilisks. Muahahahahaha!

[Quoth The Raven]

50% of all chests are now level 35 mimics. 50% of the remaining have rot grubs.

Heya me is mimic.