Each class also has three of their own skill trees, each containing 10 skills: these skills can be learnt and then used by investing skill points. Characters receive one skill point each time they gain a level-up, and skill points can also be awarded once in each difficulty level for completing the following quests:
Since 1.13, stat and skill points can be reset as a reward from Akara for cleansing the Den of Evil in each difficulty level, allowing the player to redistribute all points previously allocated. Characters who completed this quest in all difficulty levels before 1.13 will only receive this reward in Hell. In Expansion games, since 1.13 stat and skill points can also be reset by using a Token of Absolution.
Although characters can only invest 20 points in each skill, their level can be increased further by applying various skill bonuses:
Active skills require an action to be taken to use them. All active skills require mana to use, with the exception of the common skills mentioned earlier, Sacrifice, level >12 Magic Arrow and level >8 Double Swing. Skill icons are red if they cannot be used, either due to lack of mana or a required item, an active delay or because it cannot be used in town.
Buffs are active skills which apply a positive effect to the user or to the user and their allies for a duration after being used.
Debuffs are active skills which apply a negative effect to the user's enemies for a duration after being used.
Passive skills require no action to apply their bonuses. Passive skills don't require mana to use, and only apply to the user or pet. Passive bonuses are based on both skill points invested and skill bonuses applied.
Synergy skills apply benefits to other skills based on the number of points invested in the synergy skill. Skill bonuses do not increase synergy bonuses. Most synergy bonuses are mentioned in the skill description, but the following skills also apply hidden bonuses based on the number of points invested in them:
Offensive Auras and Defensive Auras apply positive passive bonuses to the user or to the user and any allies, or negative passive bonuses to any enemies within their radius of effect, as long as the aura is selected on the right mouse button. Auras do not cost mana, with the exception of Prayer.
Using other class skills
Each class can gain access to the skills of another by equipping certain items with the following: