The most common perils of a dungeon-delving career are probably injuries and death. But sometimes special effects kick in that don't kill a delver outright, but do make life a little more difficult for a while. Here are some of them.
The living dead hunger for the life-force of those still living. Any undead monster greater than ghouls and ghasts are likely to drain the living essence out of their victims. The effect is called Drain, and is normally inflicted one or two levels at a time. If the total of Drain levels exceeds the level of the character suffering from them, he is cursed to a living death.
Each level of Drain causes -1 to attacks,
saves, and hit points recovered (both for spells and for any single
stretch of rest & recuperation), and it blocks the highest available
spell slot from being used (so with enough levels drained, you can lose
all spells and it may be virtually impossible to recover hit points).
Each week of complete rest reduces the Drain level by 1. If the PC goes a
month without eliminating a Drain level, all remaining levels convert
to permanent level loss.
A Remove Curse spell converts all Drain
levels into temporary level loss (which, after you convert the attack
& save stats, is usually a big improvement). A week of rest recovers
one level, but going a month without recovering a level renders all
remaining temporary loss permanent. XP gained while level is temporarily
reduced should be recorded separately, added to the PC's total only
when all temporary levels are either eliminated or converted.
This ancient curse manifests the hunger of the grave, forever striving to devour the living. The victim of grave rot gains no benefits from magical healing and has only a 10% chance of recovering any hp on any given day of rest. Wounds and even minor abrasions begin to fester, so that the character soon looks and smells ghastly. Each day the character bears wounds and fails to recover hp, he loses 1 Charisma. When hp is full, he recovers 1 Charisma per day of rest.
The victim is helpless for 1d4+2 turns after combat ends. Any Cure spell can end this effect in lieu of other effects.
A stunned combatant can't attack, reduces speed to 1/3 normal, suffers -4 on AC & Saves, and can't focus on magic at all. This status normally lasts only a single round.
Each level of Weakness causes -1 to attacks and damage. Weakness persists for 1d6 turns. If additional levels are added before the first levels are fully recovered, roll duration again and start the count anew. If a character suffers more levels of weakness than her level, she recovers from half when the duration lapses, and compare again the following turn.