Your score is equal to:
- (Pwr+Dex+Arm)*10 +
- Gold*10 +
- WeaponCost +
- EquipmentCost +
- lvl*100 +
This is all then multiplied by the difficulty multiplier.
- Easy: 50% score, recover (MaxHP/5) per explore.
- Normal: 100% score, recover (MaxHP/10) per explore.
- Nethack: 150% score, recover (MaxHP/999) per explore.
Whether an attack hits or misses usually depends on the attacker's Dex and the target's Arm. More specifically, if an attack's accuracy (for example, Dex+d8 for a Warrior's Bash) is greater than or equal to the target's armor (mostly the Arm stat, but also bonuses like the Warrior's Guard skill), then the attack hits. If an attack misses, the target's armor is usually reduced by 1 or 2 points (depending on the enemy and the attack used), so if you keep missing you'll eventually be able to land a hit. There are a few exceptions though, using certain skills against certain enemies won't reduce armor at all on misses.
If an enemy successfully hits you, temporary armor effects (both bonuses and penalties) are removed, leaving your total armor equal to your Arm stat.
In addition to blocking attacks, the Arm stat is also used for damage reduction. Not all classes get damage reduction from Arm, however. Wizards, Rogues, Monks, Bards, Clerics, Necromancers, Druids, Darkfolk, Oni, Espers, and Saiyans get damage reduction equal to Arm/3, while Rangers get Arm/5 damage reduction in the Dungeon, Arm/4 in the Hollow Earth, and Arm/3 in the PentPlane. Warriors, Mercenaries, Blackguards, Paladins, and Enforcers get damage reduction from their equipment instead. Red Knights, Lime Knights, and Avengers get no damage reduction at all.
Note that damage reduction is based on your Arm stat, not your total armor. So having your armor increased or reduced during a fight only influences blocking, not damage.
Health potions restore ((lvl+2)*10) HP, and set your temporary armor to 5 as an added bonus (or penalty, if you've increased your temporary armor beyond that through one of your skills).
When you die, you have a chance to continue on using your second wind, though you lose 2/3 of your gold. After using it, you're unable to use it again until you move on to the next area, or until you defeat one of the gods in the PentPlane. In addition to bringing you back to life, using your second wind in the Dungeon gives a hidden 25% bonus to your Pwr and Dex until you leave the Dungeon. Using it in the Hollow Earth gives a 15% bonus, and in the PentPlane there's no bonus.