Backstab is an ability, usable by thieves, thief kits (except swashbuckler), and Stalkers, which enables them to plunge their weapon into an unsuspecting opponent's vital point, inflicting critical damage to the target.
Traditionally, a thief uses their special ability Hide-in-Shadows to Stealth, then attacks the enemy from behind in an attempt to inflict multiplied damage (see table below). Stealth will start to wear off as soon as an attack is initiated, but will last until first attempted attack. A successful hit while stealthed will result in an automatic backstab, however the thief will immediately leave Stealth regardless, even in the case of a miss.
Backstab Elligible Weapons Edit
You can backstab only with the basic Thief melee weapon set: Long Sword, Short Sword, Katana, Wakizashi, Ninja-To, Scimitar, Dagger, Club, and Quarterstaff. Even if you can use other weapons(i.e. in case of Fighter/Thief multiclass, or thanks to Use Any Item) you cannot backstab with them.
Backstab Damage Formula Edit
(weapon damage + damage bonuses) x multiplier + strength bonus
- weapon damage is the regular weapon damage range. Bonuses from enchantments and any extra regular damage(i.e. +1d4 Piercing from Staff of the Ram) are included, hovewer elemental damage(i.e. +1 Cold Damage from Varscona) is not.
- damage bonuses are damage bonuses from class kits, weapon specialization, and weapon style bonuses.
- multiplier is the backstab multiplier. See bottom of the page.
- strength bonus is bonus damage from high Strength.
The entire backstab damage(strength damage bonus included) will be again doubled in case of a critical hit.
Note that for regular Thieves and Thief mutliclasses, most of the factors in the formula are constant or almost constant: only the Assassin Kit has applicable 1 bonus damage from Kits and any Thief that can backstab is at most Trained in weapons they're using(which means no damage bonus from weapon specialization) Fighter/(Mage/)Thief multiclass can be Specialized which means 2 extra damage from weapon specialization. The only Weapon Style which has a damage bonus(of 1) is the Two-Handed Weapon Style, which requires you to use a Quarterstaff, as it's the only Thief melee weapon that is wielded with both hands.
Therefore, for regular and multiclass Thieves, the most important factor when it comes to backstab damage is raw weapon damage.
Backstab Success Chance Edit
Since a backstab occurs automatically with a successful hit, success chance can be increased by lowering THAC0, which is the same as increasing to-hit. In other words, items that increase 'to-hit' actually decrease THAC0 which is favorable when calculating the dice rolls. There are several ways to decrease THAC0:
- Gain levels, which decreases THAC0 for thieves every two levels (thieves have a THAC0 progression of 1:2, reducing THAC0 by 1 point every 2 levels).
- Invest a proficiency point into a backstab-capable weapon proficiency, to eliminate penalties.
- Equip enchanted weapons, which provide a to-hit bonus, thereby decreasing THAC0.
- Roll an elf, whose racial bonus provides a +1 to hit bonus with short swords and long swords, thus decreasing THAC0 by -1.
- Refrain from duel-wielding weapon proficiency since backstab-capable Thieves can only invest 1 proficiency point, resulting in -2 to hit for the main hand and -6 to hit with the off-hand. This increases THAC0 by 2 points for the main hand and 6 points for the off-hand.
- Obtain high Strength, which decreases THAC0 at certain levels. For example, Half-Orcs receive a +1 Strength bonus, and can start the game at 19 Strength, giving a -3 Strength modification to THAC0. By comparison, an Elf at 18 Strength only gets a -1 Strength modification to THAC0. Reading the Manual of Gainful Exercise can increase strength from 18 to 19 decreasing THAC0 from -1 to -3.  Spells such as Strength (spell) set the target strength over 18, which can provide THAC0 bonus if the thief has comparatively lower Strength. In BG2, equipping Girdle of Hill Giant Strength or drinking the Potion of Hill Giant Strength increases strength to 19, providing the associated THAC0 bonus.
- Wear enchanted items, such as Legacy of the Masters, and Gauntlets of Weapon Expertise which lower THAC0.
- Consume the Potion of Power which modifies base THAC0 to 80%.
- Choose the thief kit Assassin(BG:EE, BG2:EE, BG2) when rolling a new character, which has a +1 to hit bonus, thereby decreasing THAC0 by -1.
Additional backstab opportunities Edit
Instead of using Hide-in-Shadows, a thief can use Invisibility to create a backstab opportunity. The advantage to this method is that it can be done while in the direct line of sight of enemies while in the midst of combat. Mage and priest invisibility spells would work for this purpose, as would drinking a Potion of Invisibility.
The Dagger of the Star has a chance to cast invisibility upon the wielder when attacking, thereby creating a backstab opportunity.
The high level ability Assassination allows for a full round of attacks using the backstab multiplier (without the need to stealth or be invisible). Using an Oil of Speed potion or Improved Haste spell doubles the number of attacks per round, theoretically doubling the number of backstab attempts while using Assassination.
Characters concealed by Mislead can backstab over and over again due to the effect of the spell: it reapplies invisibility almost instantly after attack and cannot be dispelled if decoy was hidden away from the enemy and character is protected against divination spells.
Multiplier table Edit
|Level||Thief Backstab||Assassin Backstab||Stalker Backstab||Shadowdancer Backstab (BG:EE)||Shadowdancer Backstab (BG2:EE)|