Each of the six schools of magic in The Elder Scrolls V: Skyrim is useful and worth checking out at some point. With enough knowledge and experience, it is not uncommon to find completely broken ways to abuse various spells that can be learned in the great, cold north of Tamriel.
The one most attuned to the inclinations of devious Dragonborn mages, or even thieves, is Illusion. This sinister school of magic allows players to target friends and foes alike with effects such as Calm, Fear, Courage, and Frenzy. It also lets one Muffle their footsteps or turn completely invisible. Those who enjoy slaying their foes outside of combat, as well as laughing at them from the shadows, should definitely try an Illusion playthrough at least once. There is lots of information to take advantage of since players have been enjoying Skyrim for a full decade.
10 Changes From Past Games
The Illusion skill has existed in past games of the series, however, there were some big changes made from The Elder Scrolls IV: Oblivion. Light magic, such as Candlelight, as well as Paralysis, have moved to the Alteration skill. The effect known as Demoralize, which causes targets to flee in terror, has been aptly renamed "Fear". Other types of spells have not returned, to the disappointment of many.
The first of these is Charm, a spell that only has an effect on a mechanic not appearing in Skyrim that pertains to dialogue skill checks. The next is Silence, the bane of mages, for it stops a target from casting spells for a short period. Lastly, Chameleon can allow the player to camouflage into the surroundings. Similar to Invisibility, though the player can interact with objects without the effect being dispelled, making it arguably better despite rarely concealing one's form completely.
9 Quests For Free Illusion Level-Up
Besides casting spells, and a few other methods, one way to gain some quick experience in Illusion is to hunt down the Master Vampire for Sybille Stentor, the court wizard in Solitude. She usually hangs out in the Blue Palace.
After slaying this bloodthirsty fiend and returning to her with the good news, she will grant the player a free skill-up in Illusion. While in Solitude, the Dragonborn can hit up the local Bards College and speak with Pantea Ateia for the quest to retrieve her flute, which itself nets the player a free level in every skill under The Mage playstyle.
8 Main Use Of Illusion Spells
Despite other spells of this school being more useful in slaying foes directly, the majority of the spells to be found here are those that focus on manipulating both allies and adversaries. Spells like Calm can ease the aggression if one accidentally angers an NPC. While others like Frenzy can entice a target to attack all those around them blindly.
There are also the Courage and Fear spells, that can strengthen a target's resolve to stand and fight or force them to flee respectively. Because of all these traits, one can orchestrate the flow of battle from wherever they please.
7 Stealth Applications
The most notable of all the Illusion spells is the infamous Invisibility. Able to allow one to completely disappear from sight, it is an unparalleled asset for stealth, regardless of the kind of offense one is running. Be a combat stealth mage that zaps enemies from the shade or a Sneak-thief ending lives with well-placed snipes, it matters not.
Being unseen offers tremendous benefits for such playstyles. Players should also remember the Muffle spell, which makes their footsteps soundless. In conjunction with Invisibility, this offers a way to essentially fade into nothingness until one decides to pounce upon their prey.
6 Perks
The perks of the Illusion skill tree usually offer general buffs like reducing Magicka cost and increasing the level of targets that can be affected by spells. Although, there are a few that players should be sure to take special note of when considering their playthrough.
Quiet Casting is a great one that pairs with stealth builds. It accordingly lets one use spells without making any noise, an ideal trait for those seeking to stay hidden. There is also the immensely broken Dual Casting, which when applied to Illusion spells often lets the weaker versions be overcharged and outperform the higher tier ones for a fraction of the cost.
5 Who To Train With
Players can potentially level up their Illusion, if they have the coin, with a select few individuals well versed in the ways of this school. Atub, an Orc wise-woman residing within the Largashbur stronghold in The Rift, is an expert with Illusion spells and can impart some of her wisdom to the player.
Drevis Neloran is a Dunmer mage who can be found at the College of Winterhold. He is a master of Illusion and can train the Dragonborn accordingly. He also sells spell tomes for this school and can offer one the quest for a master tier Illusion spell.
4 Easy Experience Gain
Due to many of the spells in the Illusion skill being non-hostile, they can be used openly on NPCs without any fear of gaining a bounty. This is, in fact, a great way to level up very quickly.
Spells like Courage, Rally, and Calm can alternately be cast onto anyone within sight repeatedly. Some great places to do this are in the palaces of Jarls, in the middles of towns, as well as many inns.
3 Mildly Outraged & Impressed
When casting such spells on NPCs, they may react in an annoyed manner and say "Hey, I didn't ask you to magic me". They won't ever get angry enough to turn hostile, however, since the player isn't actually doing anything to harm them or their surroundings.
If one's level in Illusion is high enough, city guards may make mention of it, saying "You're the one that casts those illusions. Impressive." This amounts to only a mild dialogue change, though it's sometimes nice to be noticed for one's talents.
2 Deadly To Birds & Fish
Even though the spells in the Illusion school don't actually deal damage, they can still be harmful to the more fragile members of Skyrim's ecosystem. The impact caused by spells likely has some sort of physics applied to them that lets the game know they made contact with something.
This initial physical impact is what may allow Illusion spells to kill birds, such as the hawk, bone hawk, and Felsaad tern. They can also kill salmon and other small creatures, though none that can actually attack or be counted as an enemy.
1 Combination With Conjuration
For a magical combo that will allow the player to breeze through dungeons without ever having to kill an enemy themselves, the Dragonborn should try combining Illusion and Conjuration. By summoning allies like Flame Thralls or a Dremora Lord, players can then buff them with higher-level versions of Courage if they have the Master of the Mind perk that lets them target creatures they normally would not be able to.
Additionally, the master tier spell Call to Arms gives targets upgraded combat skills, more health, and more stamina, which can boost summoned allies to the point where they can take out some bosses by themselves. To ensure that one stays out of the adversary's gaze, the player can also cast Invisibility and cackle from the shadows as their puppets dance.