An oskill in Diablo II is a bonus to a specific class skill with no class restriction, which allows characters to use an oskill even if it is not normally available to their class. Oskills were added in the Lord of Destruction expansion.
Oskills do not appear in the character's skill tree, and a character cannot spend skill points to improve oskills. Oskill levels are improved only by "+ to all skills" bonuses. If the character does not have the skill, the base level for that skill is considered 0.
Otherwise, oskills function as they would for their native class. They can be assigned to left-click and right-click buttons as well as hotkeys, if the skill normally allows it.
They only appear on specific set bonuses, unique equipment, and Rune words.
Same class cap
Oskills are capped to +3 skill levels if used by their native class. For example, the four-piece set bonus for Trang-Oul's Avatar is +10 to Meteor. Classes other than Sorceress will be able to cast a level 10 Meteor (or higher, with + to all skills) while wearing four pieces of Trang-Oul's. A Sorceress wearing the same will receive only +3 to her existing Meteor skill, however. This allows oskill bonuses to be large enough to be useful to other classes without being overpowered for their native class.
The cap is applied on the whole character, not on the source of the oskill. This means that even when a character is using multiple sources of the same oskill (this is possible only in the case of Barbarian wearing two Call to Arms weapons), he will only gain a maximum of +5 to Battle Orders in total: +3 from the Call to Arms oskills and +2 from the Call to Arms +all skills.
Examples
A common application of oskills is switching to a Call to Arms weapon, using the Battle Command and Battle Orders oskills granted by Call to Arms, then switching back to the main weapon, retaining the increased life and mana pools from Battle Orders. This technique is especially potent for characters with many +skill bonuses, such as Sorceresses and other spellcasting based builds.
Another common application of an oskill is Enigma armor, which allows any class to cast Teleport.
Oskills are the basis for some unusual builds, such as a Sorceress specializing in Enchant using a Passion weapon's Zeal oskill to deliver fast melee attacks, or a Barbarian specializing in normal (non-skill) weapon attacks with one weapon using a Beast weapon's Werebear and Lycanthropy oskills to increase defense and maximum life.
Table of oskills
| Bonus | Oskill | Native class | Equipment | Notes |
|---|---|---|---|---|
| +7–14* | Arctic Blast | Druid | Frostwind unique sword | |
| +2–6* | Battle Command | Barbarian | Call to Arms rune word weapon | |
| +1–4* | Battle Cry | Barbarian | Call to Arms rune word weapon | |
| +1–6* | Battle Orders | Barbarian | Call to Arms rune word weapon | |
| +1 | Berserk | Barbarian | Passion rune word weapon | |
| +2 | Critical Strike | Amazon | Peace rune word body armor | |
| +1–6* | Critical Strike | Amazon | Insight rune word weapon | |
| +30 | Enchant | Sorceress | Horazon's Splendor full set bonus | Warlock only. |
| +6* | Evade | Amazon | Hustle rune word armor | |
| +3–6* | Feral Rage | Druid | Wolfhowl unique barbarian helm | Barbarian only. |
| +3 | Fire Mastery | Sorceress | Trang-Oul's Avatar full set bonus | Necromancer only. |
| +13* | Fire Wall | Sorceress | Trang-Oul's Avatar 3-piece set bonus | |
| +18* | Fire Ball | Sorceress | Trang-Oul's Avatar 2-piece set bonus | |
| +3–5* | Guided Arrow | Amazon | Widowmaker unique bow | |
| +10* | Hydra | Sorceress | Dragonscale unique paladin shield | Paladin only. |
| +12–18* | Inferno | Sorceress | Flamebellow unique sword | |
| +3 | Lycanthropy | Druid | Beast rune word weapon | |
| +3–6* | Lycanthropy | Druid | Wolfhowl unique barbarian helm | Barbarian only. |
| +10* | Meteor | Sorceress | Trang-Oul's Avatar 4-piece set bonus | |
| +1 | Teleport | Sorceress | Enigma rune word body armor | |
| +2–6* | Valkyrie | Amazon | Harmony rune word weapon | |
| +1 | Vengeance | Paladin | Kingslayer rune word weapon | |
| +1 | Warmth | Sorceress | Enlightenment rune word body armor | |
| +3 | Werebear | Druid | Beast rune word weapon | |
| +3–6* | Werewolf | Druid | Wolfhowl unique barbarian helm | Barbarian only. |
| +1 | Whirlwind | Barbarian | Chaos rune word weapon | Assassin only. |
| +1 | Zeal | Paladin | Passion rune word weapon |
* capped at +3 for native class