Ring of sustain abilities
|This ring protects its wearer from the loss of their strength, dexterity and intelligence.|
The ring of sustain abilities 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 abilities does not affect the permanent loss of abilities that might be incurred by mutations.
If you happen to have one in your inventory, you could put it on if you come across a monster capable of draining your stats or making you sick. Stat losses incurred through routine exploration are largely negligible, however, so most characters need not bother; characters with particularly low stats (such as a berserker with low intelligence) may wish to have one on hand for such occasions, as stat zero is extremely unpleasant.
Deep dwarves (who do not regain stats naturally) and mummies (who can only regain stats by waiting or spending a permanent MP) might consider wearing one of these rings, and even for them, a good resistance is usually a better choice, since stat drain is rarely immediately life-threatening.
However, the Deterioration mutation makes these rings become far more useful. Level 1 of that mutation is generally just annoying, but at levels 2 and 3, it becomes almost a necessity to wear one of these rings until you can get rid of the mutation. A deep dwarf with any level of deterioration will nearly always want to be wearing a ring of sustain abilities.
Another situation that may merit a ring of sustain abilities is the exploration of the Tomb, where you will encounter large numbers of death curses, many of which will have a small, but significant chance of reducing your stats. A ring of sustain abilities will make the stat losses more manageable.
If you want to run the extended endgame and explore Hell, you'll need sustain abilities to block the frequently occuring stats reductions by Hell's mystical force. Since randarts with this quality are very, very rare and the only Unrandart delivering SustAb is the Orange crystal plate armour you'll need probably this ring.
In 0.17, these rings will be renamed to "sustain attributes".
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.