A delayed instadeath is an effect that is not immediately fatal, but will cause you to die instantly after some delay period, regardless of how many hitpoints you have at the time. These effects are generally treatable, so long as you are prepared, and act quickly.
Although the term delayed instadeath sounds self-contradictory, it is the accepted term in the roguelike community. Insta[nt] can be understood as referring only to the final reduction of hitpoints, which occurs in one fell swoop once the delay period is over.
Delayed instadeaths are regarded as major problems by your god, so prayer will normally save you, as long as it is otherwise safe to pray.
The following delayed instadeaths exist in NetHack:
- Turning to stone as a result of being hit by a cockatrice's special attack or eating a cockatrice egg. The standard cure is to eat a lizard corpse. Vegetarians can quaff a potion of acid instead. Acidic corpses are also useful, and other remedies exist.
- Sliming (turning into green slime). Curable by setting yourself on fire or casting Cure Sickness.
- Food poisoning from eating an old corpse or disease from the sickness attack of Juiblex, Scorpius, Demogorgon, or Pestilence, or as one of the effects of applying a cursed unicorn horn. Curable by applying a non-cursed unicorn horn (risky, as it may fail) or casting Cure Sickness.
- Sinking in lava. Fix this by praying, zapping a wand of cold downwards, or teleporting.
- Strangulation, from wearing an amulet of strangulation. Instantly curable by removing the amulet, but amulets of strangulation are normally generated cursed.
- Eels, krakens, and couatls can cause delayed drowning.
- Purple worms and trappers can digest the player, a delayed instadeath if the monster is not killed. Note that the exact time of death is random and based on attributes.
Prayer will not save you from the last two delayed instadeaths.