|This ring protects its wearer from the loss of their strength, dexterity and intelligence.|
The ring of sustain attributes cuts any temporary loss of stats in half, rounding down. Note that most sources of stat loss cause you to lose a single point, so this ring completely negates those (e.g. sickness and the Deterioration mutation).
A ring of sustain attributes does not affect the permanent loss of stats that might be incurred by mutations.
Temporary stat loss is restored as you gain XP, which means that characters experiencing low levels of stat loss can simply kill monsters to restore their stats without needing sustain attributes. However for characters with at least one low stat (e.g. a berserker with low intelligence), sustain attributes can help to avoid getting stat zero, which has extremely dangerous side-effects. Characters that experience larger amounts of stat drain, such as those with higher levels of the Deterioration mutation or those regularly using a Crystal Ball of Enery or the Staff of Wucad Mu, will also find this ring useful.
In some extended branches of the game, you experience far more stat drain than usual. In Tomb you encounter large numbers of death curses, many of which will have a small but significant chance of reducing your stats. In Hell the frequent effects the you experience from Hell's mystical force include potentially large stat drain. It's important to watch your stat levels when visiting these branches, putting on sustain attributes as necessary. Your effectiveness is greatly reduced when stats are much lower, and for characters who have a low stat (either permanently or temporarily from previous stat drain), the ring can prevent reaching stat zero.
Prior to 0.17, this item was called a ring of sustain abilities.
Prior to 0.15 you received a cumulative effect for wearing two rings, reducing stat loss by 75%, thus entirely negating all stat damage dealt in increments of 3 or less.