Skills

Overview
In Ragnarok, there are generally 3 types of skills: Passive, Active, Offensive. Passive skills are always "activated" although they may require the user be attacked or otherwise influenced by other environmental effects in order to go off. Active skills must be manually activated by the player- some have a set time period in which they stop by themselves, others can be manually deactivated, and some are one-time-use skills that require manual activation each time the player desires to use them. Active skills do not inflict actual damage, differentiating them from Offensive skills. All Offensive skills are also Active skills, but not vise-versa. Finally, Offensive skills are simply Active skills that also do damage to other players and/or monsters. Skills can be further broken down into other sub-categories such as Melee, Ranged, Magic, Supportive, etc. Skills in these categories also fall under one of the three "main" categories listed in the previous paragraph. Some skills fall under multiple sub-categories as well. Ranged skills do not require the player to be standing adjacent to the target, whereas Melee skills generally do. Magic skills almost always involve a Cast Time and are usually Ranged. Supportive skills are termed due to their helpful effects they give to a single player or group of players, enhancing their attack and defensive capabilities.

Skill Use Phases
Skill use is a five-step process, three points seperated by two phases.

Skill used Cast time Skill activation Cast delay Skill use complete Cooldown
 * Skill name appears above character's head.
 * Cast bar is visible above character's head.
 * Skill name appears above character's head again.
 * No visible indication. When the delay ends you will be able to use another skill.
 * No visible indication.
 * The specific skill can not be reused for a fixed time. (not all skills have cooldowns)

Phases in Detail
Skill Used

This is when the character uses the skill. SP cost and other casting costs are checked, but do not take effect. If the character cannot pay any of the costs, the skill will not activate.

Cast Time

During the cast time, the character cannot move, cannot attack and cannot use other skills. If the character takes damage during cast time, the skill is canceled (exceptions: wearing a Phen Card or Bloody Butterfly Card, being Sacrificed by a Crusader/Paladin, or while casting certain skills). If a skill has no base cast time or modifiers reduce the effective cast time to 0 or less, no cast bar appears and the cast time phase is skipped entirely.

Cast time is indicated by a "progress bar" above the character's head, sometimes called cast bar. The bar starts out black and is filled with green as cast time proceeds. When the cast bar is completely green, cast time ends. Some skills do not have a cast bar, even though they have a casting time, such as Bowling Bash and Brandish Spear.

Cast time is composed of "Variable Cast Time" and "Fixed Cast Time". As the names imply, Variable Cast Time depends on the stats and gear of the caster, while Fixed Cast Time is constant for a given skill. A small number of effects can reduce Fixed Casting Time. For most skills, Fixed Cast Time is 20% of the total cast time, with the remainder being variable.

Variable cast time is reduced by DEX, and also INT at half the amount. Cast Time Calculation castTime = (1 - SQRT((DEX * 2 + INT) / 530)) * (1 - sum_castReduction/100%) * baseCast * 0.8 + (1 - max_fixedReduction/100%) * baseCast * 0.2 baseCast = base casttime of a skill. sum_castReduction = Sum of reduction for variable casttime (like Suffragium, Magic Strings, isilla card effect or kathrene keyon card) max_fixedReductrion = Highest reduction modifier of fixed casttime (for example if both Sacrament (50%) and Radius (20%) are active only Sacrament will work) To reduce all variable casting time with stats you need a combination of DEX and INT so DEX*2 and INT is at least 530 ((DEX*2+INT) = 530). Some examples how you could reduce all variable casting time: Cast time is only calculated once. It ignores changes to the modifiers during cast. This means it is possible to start casting and equip a phen clip afterwards to get the phen effect for most of the cast time without the cast time increase.
 * 530 INT
 * 265 DEX
 * 170 INT and 180 DEX
 * 190 INT and 170 DEX

Notes Modifiers
 * Free Cast skill allows movement and attacking while casting.
 * Phen Card and Bloody Butterfly Card both allow taking damage without being interrupted (but not during War of Emperium)
 * The Crusader skill Sacrifice allows the caster to take damage without being interrupted (works in War of Emperium)
 * Certain skills cannot be interrupted (generally ones intended to be used by classes on the front lines)
 * 1) Bloody Butterfly Card: +30% variable cast time
 * 2) Magic Strings: see skill description
 * 3) Phen Card: +25% variable cast time
 * 4) Suffragium: -15% variable cast time * Skill Lv.
 * 5) Tower Keeper Card: -5% variable cast time
 * 6) Kathryne Keyron Card: -1% variable cast time per upgrade of the headgear
 * 7) Orlean's Gown [1]: +15% variable cast time

Bear in mind that although Bloody Butterfly Card adds 30%, the full set gives a bonus of -15% meaning that it would only be an end result of +15% (vs. the Phen's 25%).
 * 1) Foresight: -50% variable cast time

Magic Strings and Foresight are treated as separate factors in the calculation; they are not added to the other modifiers.

Skill Activation

SP cost and other casting costs are checked again. If the character can pay the costs, they are paid and the skill takes effect. If not, nothing happens. If the character is inside a chat room, no skill effect happens, but the costs are paid as usual.

Cast Delay

During cast delay, the character can move and attack freely, but cannot use skills. There is no visible indication of cast delay.

Cast delay is often called skill delay for non-magic skills. Cast Delay Calculation The base delay depends on the skill and skill level. Cast delay = base delay * (1 - x * 0.01) x is sum of modifiers In English:

Modifiers Cooldown
 * Start with base delay.
 * Reduce by x%. (Rounding and other details unknown)
 * Magic Strings: see skill description
 * Kiel D-01 Card
 * Expert Ring

For a fixed time after the player has used the skill, the player will be unable to use that same skill again. They may however use any other skills they wish.

There is no way to reduce a Skill Cooldown. They are usually set on a per-skill basis and occasionally vary by skill level used.
 * Note: Almost all 1st and 2nd class skills have no cooldown.

Reference
iRO Wiki