Combat system

This article is a work in progress!

Attack Roll

Attack Rolls, or AS/DS Checks, are the most common form of combat resolution in GemStone IV.

AS/DS Check

A typical attack roll looks like this:

You swing with a fist-scythe at a lesser orc!
AS: +109 vs DS: +44 with AvD: +39 + d100 roll: +70 = +174
  ... and hit for 20 points of damage!
  Wild slash scratches the back of the lesser orc's hand.
Roundtime: 5 sec.

In an attack roll, the attacker's Attack Strength (AS) is compared against the defender's Defensive Strength (DS), plus an Attack versus Defense (AvD) value based on the weapon type and the defender's armor. Finally, a random number from 1 to 100 (d100) is added to the result. If the final result is greater than 100, the attack is successful. The higher the result is, the more damaging the attack will generally be.

Attack Strength is mainly based on the attacker's Weapon skill and their stance.

Defensive Strength is mainly based on the defender's training in various defensive skills such as Dodging, Shield Use, and Weapons, as well as their stance. Armor does not add directly to Defensive Strength (aside from possible enchantment bonuses), but is a major factor in determining how much damage is taken if an attack does land.

Evade-Block-Parry

There is a chance for the defender to avoid an attack outright by evading, blocking, or parrying it, avoiding the AS/DS check. These defenses are passive, so players do not need to enter any commands for them to activate.

You thrust with a spear at a kobold!
The kobold awkwardly scrambles to the right and blocks the attack!

Evade

The first step in combat will be the opponent's opportunity to evade an attack altogether. Evasion success will be based upon a combination of factors, including the character's Dodging skill, armor hindrance, encumbrance, Agility, Intuition, shield size (increased hindrance with larger shields), stance, the level of the opponent, and some spells, such as Mobility, Mass Blur, and Song of Mirrors.

Block

If the Evade attempt fails, the next step is the opportunity to block the attack. In order to block, the character must have a shield in their left hand. The Block attempt is based on a combination of factors, including the character's Shield Use skill, armor hindrance, encumbrance, Dexterity, Strength, shield size (bonus for the larger shield), stance, and the level of the opponent. Shields provide more benefit when blocking missile and bolt spell attacks than they do against melee attacks. It is not possible, however, to block a bolt spell outright without using a specially enhanced shield.

Parry

Finally, if the attack has not been evaded or blocked, the opponent will attempt to Parry. The character must have a weapon in their right hand to parry (bonus for an additional weapon in the left hand). It is not possible to parry missile weapons or bolt spells without using magically enhanced weapons specifically designed for such parrying (see also: Runestaff). The parry attempt is based on several factors, including the character's relevant Weapon skill, armor hindrance, encumbrance, Dexterity, Strength, stance, and the level of the opponent.

Damage Calculation

Location

If an attack is successful, it deals damage to a random location on the defender's body. Players can AIM or AMBUSH an attack against a specific location, increasing the chance of hitting it, but doing so consistently requires extensive training in the Combat Maneuvers and Ambush skills and is mainly useful for characters above level 20.

When not aiming specifically at any location, the likelihood of hitting each body part is approximately as shown in the following table:

Location	Chance
arms (either)	19.7%
legs (either)	16.5%
chest	14.7%
abdomen	12.1%
back	10.1%
hands (either)	9.0%
neck	7.4%
eyes (either)	5.3%
head	5.2%

Damage

Main article: Standard damage calculation explained

The system takes the result of the successful attack roll and subtracts 100, then multiplies the weapon's damage factor to obtain the raw damage. Based on the raw damage and the armor type, the system then assigns critical damage with some minor random variation. The defender takes HP damage equal to the raw damage plus the critical damage, and suffers a wound to the specific body location based only on the critical damage and its type (for example, a slashing weapon will deal different criticals than a fireball).

Redux

Main article: Redux

Characters with extensive physical training may reduce the damage taken by a successful attack roll. This effect increases with training in physical skills and decreases when learning magical spells.

Warding roll

The second combat resolution type occurs when a combatant casts a warding spell at an opponent. Here, CS is always compared against TD or Target Defense, to resolve success or failure of the attack. This type of resolution looks like this:

CS: +141 - TD: +128 + CvA: +25 + d100: +60 == +98

This attack likewise has four components which function similarly to the AS/DS resolution type, each component possibly comprised of several factors.

1. CS: +141
   CS, or Cast Strength has been calculated to be 141 for this attack. Factors that make up this component include spell ranks, attribute bonuses like WIS or AUR, and certain spells such as Elemental Targeting or Mystic Focus which can add to the spell's power.
   
   
2. TD: +128
   TD, or Target Defense has been calculated to be 128 for this attack. Factors that make up this component include character or creature level, attribute bonuses like WIS or AUR, and those defensive spells that help the opponent ward off spells.
   
   
3. CvA: +25
   CvA, or Cast versus Armor, is a numerical value that shows how hard it may be to penetrate armor with warding magic.
   
   
4. d100 roll: +60
   Again, the attack is randomized by a d100 (random number between 1 and 100).
   
   == +98
   In this example the opponent successfully wards this spell and will suffer no ill consequence. It is also not likely that the combatant will see success using this tactic against this opponent, there is only a 37% chance of this attack being successful.

Unarmed combat or UAF

The third combat resolution type occurs when a combatant uses the unarmed combat (referred to in general as UAC) based on their brawling skills against an opponent. There are several subtleties in the unarmed combat system that make it a bit more complex than just swinging a blade or tossing a bolt spell. Here, UAF, or the unarmed attack factor for the attacker is always compared against UDF or unarmed defense factor of the defender, to resolve success or failure of the attack. This type of resolution looks like this:

UAF: 29 vs UDF: 31 = 0.935 * MM: 125 + d100: 92 = 208

This attack again has four components which function similarly to the preceding resolution types, each component possibly comprised of several factors.

1. UAF: 29
   The UAF or unarmed attack factor has been calculated to be 29 for this attack. Factors that make up this component include skills, attribute bonuses like STR and AGI, the enchantment properties of UAC-specific boots and gloves, and certain spells such as Strength or Dragonclaw.
   
   
2. UDF: 31
   UDF, or the unarmed defense factor has been calculated to be 31 for this attack. Factors that make up this component include character or creature level, dodge and parry abilities, shield use, the enchantment properties of various items, and those defensive spells that help the opponent's defenses.
   
   = 0.935
   In the case of unarmed combat, an interim value is calculated and shown. This interim value is simply a ratio derived from the UAF divided by the UDF. Of course, you would like this interim value to be higher than 1.0, and it has a highest potential value of 2.0.
   
   
3. * MM: 125
   MM, or Multiplier Modifier, is calculated here to be 125 and is a concept unique to the UAC system. It is a numerical value comprised of various advantages and penalties like the combatant's stance and positioning, equipment like shield or weapon held and armor worn, the opponent's stance and status (i.e. stunned or prone), and the lighting conditions in the room or area.
   
   
4. + d100: 92
   A random d100 (random number between 1 and 100).
   
   = 208
   The final result is 208 indicating a successful attack. This number is calculated by taking the interim ratio calculated earlier, multiplying that ratio and the multiplier modifier, and then adding the d100 result. The Combat System would use this number to calculate hit point damage, wounds suffered, critical ranks if applicable, and any change based on the critical suffered to the combatant's status.

Maneuvers

Resolution of combat maneuver skills such as Bearhug or Shield Bash are more streamlined. This type of resolution looks like this:

[Roll result: 109 (open d100: 56)]

This resolution has only two visible components, but there are a couple of peculiarities.

1. Roll result: 109
   Unlike the preceding combat resolution types, this one starts off with the resolution result for the attack. Again, the value to strive for is greater than 100.
   
   
2. (open d100: 56)
   And unlike the preceding combat resolution types, the concept of an open-ended d100 (random number between 1 and an unbounded value) is expressed. In simple terms, a standard d100 result is generated, and if that value is 96 or greater, another d100 value is generated. This process continues (open-ended) until the d100 roll result is less than 96. Then all the values are added together. Therefore, however unlikely it may be, it is possible to have this number show a result of 200, 300 or more!

Resources

• A beginner's guide to combat