Skyrim:Illusion

Illusion is one of the five schools of magic in Skyrim. Illusion magic focuses on changing the perception of the world from the viewpoint of the target. Increasing this skill reduces magicka cost when casting Illusion spells. The Illusion skill tree has a total of 13 perks, requiring a total of 13 perk points to fill.

In-game Description: The School of Illusion involves manipulating the mind of the enemy.  This skill makes it easier to cast spells like Fear, Calm, and Invisibility.

For historical information, see the main lore article.

Summary

Illusion contains a range of spells that play with your enemies' minds. While no Illusion spell does any direct damage, spells and perks in this school are a good supplement to Stealth-focused characters, and make stealthy play more viable for mages.

Main Effects
Progressively more powerful spells with each of these effects are available as your character develops. Some of these effects can also be produced using Alchemy and enchantments.
Pacify spells minimize aggression and cause the affected to lose the will to fight unless attacked first.
Fear spells minimize confidence and cause the affected to run away.
Frenzy spells maximize aggression and cause the affected to lose allegiance and attack anyone they see.
Rally spells maximize confidence and increase the stats of the affected and prevent them from fleeing.
Muffle helps the caster to sneak around by reducing the noise made by walking.
Invisibility removes the ability to be detected by sight, but unlike sneaking, wears off immediately if the caster touches something, casts a spell or uses a weapon.

Spell Types
For each effect type, the pattern of spells is consistent:

Target Level does not apply to Rally effects.  All missiles, area or not, are range 469 feet.

Usage
Illusion is a formidable tool against almost every enemy in Skyrim, dragons being a notable exception. It can be used on its own as a combat tool, but it is best used in conjunction with another skill to take on enemies. 

The only effect that serves as a combat tool is Frenzy, which can be used to cause groups of enemies to decimate each other. Frenzy spells can also be useful for hunting deer and other fleeing animals, as they will turn and attack you instead of running away. Furthermore, casting a Frenzy spell on someone is not considered a crime if you are hidden when you cast it (regardless of whether or not you have the Quiet Casting perk). This can make some of the Dark Brotherhood contracts much easier. 

You can simply avoid combat with Fear, or Pacify, the latter of which has the additional use of allowing you to converse and trade with otherwise hostile NPCs. Pacify spells may also allow you to set up additional sneak attacks if the first did not kill your opponent. Invisibility and Muffle can allow you to bypass enemies, even in full daylight, or setup sneak kills. Followers can be rallied to provide better protection at times too. Quiet Casting also affects use of the Thu'um, so you will be able to shout and stay undetected.

Drawbacks to the skill are that undead, Daedra, and dwarven automatons are unaffected by Illusion spells until the perk Master of the Mind is activated. Without the Quiet Casting perk, enemies will be able to hear the casting of the sneak-oriented spells Muffle and Invisibility, and may still be able to detect you.

Skill Perks
 
 
 

 
 

Spells
 
Spell List Notes
 

Magical Effects
A list of standard Illusion spells can be found on the Spells page.  The following individual effects are all considered to be part of the school of Illusion (see the individual effect pages for full details on availability; the Magical Effects article also provides a summary):

 Clairvoyance
 Rally
 Fear
 Frenzy
 Pacify
 Invisibility
 Muffle

Skill Increases
Character Creation
The following races have an initial skill bonus to Illusion:
+10 bonus: Altmer
+5 bonus: Breton, Dunmer

Trainers
Atub in Largashbur (Expert)
Drevis Neloren in the College of Winterhold (Master)

Skill Books
''2920, Sun's Dawn, v2
Before the Ages of Man
The Black Arts On Trial
Incident at Necrom
Mystery of Talara, Part 4''

Free Skill Boosts
+1 Illusion reward from Sybille Stentor for completing the quest Kill the Vampire.
+1 Illusion reward (+1 every magic skill) from Pantea Ateia (Bards College) for completing the quest Pantea's Flute.
+5 Illusion (+5 every magic skill) by selecting "The Path of Magic" when reading the Oghma Infinium after completing the quest Discerning the Transmundane.

Gaining Skill XP
Casting higher level spells gives generally faster skill increases (Novice<Apprentice<Adept<Expert<Master).
It is possible to reduce or even completely eliminate the magicka cost of spells by stacking Fortify Illusion enchanting effects, which is very helpful for Illusion training. The Secret of Arcana  power does the same thing, but only for 30 seconds.
Casting Muffle on yourself repeatedly will level up your Illusion quickly, even if there are no enemies around.
If you reset your Illusion skill after learning the master-level spells, casting Harmony repeatedly in a heavily populated area, such as Whiterun, will level up your Illusion significantly. Depending on how many NPCs the spell hits, you could level from 15 to 100 in under 30 seconds by casting the spell.
Casting Courage or Rally on NPCs is effective and is not considered a crime. Courage uses less magicka, but Rally will level the skill more quickly. However, both can rarely turn a few otherwise non-hostile NPCs hostile, such as Vigilants of Stendarr and Revelers.
If using Rally to level, try to hit as many people as possible in one shot. Casting it into groups of people will raise the skill much faster than hitting single targets.
Simultaneously casting Rout and Pacify (one assigned to each hand) on an enemy will rapidly level Illusion. Although the effects of Pacify should keep the target stationary, this is best done in a small enclosed area to ensure that you can hit the target each time the spells are cast.

Dialogue
When the player reaches a high level in this skill, NPCs (particularly guards) will sometimes comment: ''"You're the one that casts those illusions. Impressive."

Notes
Clairvoyance can be cast as long as there are people around (not counting your follower or other allies) to gain experience in the skill. Muffle and Invisibility can be cast to gain experience even if there is no one around.  All other spells must be cast on a valid target to gain experience, although this does not have to be an enemy.
Casting Invisibility without the Quiet Casting perk may allow your character to still be detected. Enemies will investigate the sound, and may find you even if you have moved from where you originally cast the spell.
Vampires are not affected by Illusion spells unless you have Master of the Mind. Even then, they are considered undead rather than people for the purposes of the Kindred Mage perk.
The Necromage perk in the Restoration tree helps with making Illusion spells work against higher level undead.
Falmer can be affected by Illusion spells without Master of the Mind, but are not affected by Kindred Mage or Animage.
Dragons are immune to all Illusion spells cast at them, regardless of skill level or perks.
Vision of the Tenth Eye can be used as a kind of Night Eye spell with some effectiveness if needed, which does not appear to increase the ability of NPCs to detect you and allows for vision beyond the limited range of Candlelight and Magelight, though its long cast time and glare from light sources can be considerable downsides.
Master-level Illusion spells do not benefit from Dual Casting; however, they can still overcome the level 50+ cap with the relevant perks and by using Fortify Illusion potions.
Casting Mayhem will often cause items in the vicinity to shift around and become irretrievable.
Quiet Casting'' also affects shouts.
There are indications in the data files that at one point in the game's development, Mysticism would have been present as a school in place of Illusion.  This is evidenced by an unused texture file containing names of all of the skills, in which Mysticism is present instead of Illusion, as well as the hardcoded order of Actor Values in the Creation Kit, in which Illusion is listed under "M" where Mysticism would go.

Bugs