Some spells improve friendly units or weaken enemy troops. Other spells do direct damage to enemies or heal allies. Most spells cost a certain amount of mana to cast. In the place of mana some classes have their own ability requirements such as Warriors, who use Rage. Some Abilities/Spells do not require mana but are instead based on a timer. Many people use the word "spells" to cover both spells and abilities.
Effect
This means how much the spell alters the target. If it is a damage spell, then the effect is how much damage the spell does. If the spell is a healing spell, then the effect is how much health is healed by the spell. If the spell is a blessing or curse, then the effect is how long the spell affects the target, in seconds.
Cast Time
The Cast Time is a measurement of the amount of time it takes from the start of casting a spell to the moment the spell is activated or finished casting. The longer the Cast Time, the longer it takes to cast a spell. You will find this time listed in your spell or abilities menu. When you are casting an ability, a Progress Indicator will pop up on the screen, indicating how close you are to casting the Ability. If you are attacked by a monster during this time, the progress bar will drop and delay the casting of your spell. You can continue to try and cast the spell or stop casting and attack the monster if you believe the delays will make it impossible to complete the casting of the spell. If you move or are interrupted by a monster's special ability (such as stun), the casting process will be completely canceled and you will have to try casting it again.
Channeling/Interruption
Many spells must be maintained or "channeled" to achieve their full effect. This applies mainly to mass-damage area-effect spells (Blizzard is an example of such a spell), although there are a few other spells that also require channeling. You will know a spell requires channeling when a progress bar appears with the word "Channeling" in it. If you are interrupted by moving, attacking, or being attacked, or if you try casting something else, the spell will not be completed and you will have to try casting it again.
Spell casting is not interrupted when leaving combat.
Channeled spells that are cancelled by movement cannot be cast while moving.
Instant Cast
Some spells can be cast instantly. This means that they cannot be interrupted by monsters, and they do not have a Casting Time. These spells can be identified in the spell book or by noting the lack of a progress bar when they are cast.
All instant cast, non-channeled spells can be cast while moving.
Casting on the Run
Some abilities can be cast while you're running. However, most require you to be standing still. The warning message that appears when you are unable to cast a spell will let you know if you must stand still, or what other error is causing you to be unable to cast the spell.
Canceling Spell Casting
You can cancel a spell by hitting the "ESC" key. Once you begin casting a spell, do not move; otherwise you will interrupt the spell. This is also a good way to stop casting if you change your mind about casting a particular spell. For instance, let's say you're a healer that is about to heal someone, but someone else heals your target before you do, or the person uses a potion. You should then start moving and interrupt the casting of your own Heal spell. This way, you will not waste Mana healing a target that no longer requires healing.
Cooldown
Cooldown is the amount of time it takes before you can cast the same spell again. This is also known as a Casting Delay. Cooldown is fixed and is unaffected by increases to Mana capacity and/or Mana Regeneration. Some spells do not have a Mana cost, and are instead limited by their Cooldown timer. Once you have used an ability, place your mouse over the ability to see how much longer you must wait in order to use that ability again.
Range
The spell book lists the range of each spell. To cast a spell on a monster, you will need to get close enough to be inside of the maximum range allotted by the spell. Typically you will want to cast your spell as far away from the monster as possible, which will give you more time to cast a second spell or do something else (like having another party member/pet taunt it) before the monster reaches you. Here is a test which will allow you to determine the maximum range: walk towards the monster and stop every few feet to click on a ranged spell. You will receive an error message each time, up until you are actually close enough to cast the spell. This is how you will know what the maximum range is. As you use your abilities more, you may find that experience allows you to judge distances and judge what the maximum range is, without doing this test.
Area of Effect Spells (AOE)
AOE spells affect multiple enemies at the same time. These abilities are useful if you encounter a pack of monsters, especially when another party member can Taunt them to him or herself, and stop the pack from swarming on the caster, or if the pack is all nearly dead. Be very careful when using these spells; they can "wake up" monsters that are neutral, and make them aggressive towards you, or generate enough "monster hate" to cause multiple monsters to attack you at once. (This will cause the caster to die almost instantly.) It's helpful to group with a Tank (A Tank is a character that can absorb massive amounts of damage without dying) to Taunt the pack and take the attention away from the caster. AOE spells have a special targeting display. Place it exactly over where you want to cast it.
Leash Spells
A Leash Spell is an ability where your character lassos the target with a stream of spell effect. Life Drain is an example of a Leash spell. You must be within range to cast and if your target moves too far away the spell will cancel (it will be out of leash range) before it reaches its full effect.
