Phantasmal Force One of eight schools of magic within Baldur's Gate 3, the illusion school provides its wielders with versatile utility spells. Whether players seek to buff their characters, debilitate foes, engage in subterfuge, or deal damage, there's an illusion spell that does the job.
Ranging from cantrips to level five, illusion spells are predominantly available to sorcerers, warlocks, and wizards, with wizards able to choose the school as their specialism, but arcane trickster rogues and eldritch knight fighters can also get some of the lower level illusion spells. Bards and clerics, particularly of the trickery domain, also have illusion options.
13 Disguise Self
Baldur's Gate 3 takes its spells, as with its world, characters, and monsters, from Dungeons and Dragons. Within the tabletop role-playing game, 
Disguise Self can serve a player well during pivotal moments of role play.
Sadly, its versatility within the tabletop game is confined within the limitations of a video game, even one as expansive as Baldur's Gate 3. Its primary use is to unlock interactions only available to certain races, for example, entering the goblin camp as a drow or the githyanki creche as a gith or to use ' 
Speak with Dead' on a character that the player killed.
12 Seeming
Seeming may be the highest level illusion spell, costing players a level five spell slot, but its use only just surpasses that of Disguise Self. While similar to Disguise Self, the increased use comes from the fact that players can use it to disguise up to four party members.
At level five, though, it is a very high price to pay for some disguises, especially as high level enemies are often able to see through a magical disguise with ease. It is, admittedly, entertaining to see party members disguised as wildly different races, though.
11 Minor Illusion
It may not be the most powerful illusion spell, to be expected from a cantrip, but 
Minor Illusion can have some useful applications. Outside of combat, it can be used as a distraction to move an enemy to an advantageous position. Players should use turn-based mode, though, as the illusion dispels after a short amount of real-time.
Within combat, enemies that fall for the illusion will occasionally waste a turn attacking it. Its use is limited, although is worth making the most of, especially for illusion wizards who are able to cast it as a bonus action.
10 Color Spray
Color Spray is a first level spell cast in a cone extending from the player. Any creatures within the cone, up to a combined total of thirty-three hit points, will be blinded for one turn.
Blinding opponents is a very effective way to debilitate them, and the beauty of 
Colour Spray is that there is no saving throw required, players can guarantee that targets will be blinded. The drawback is, of course, that it only lasts for one turn. Still, it is an effective illusion spell to utilize, especially for such a low level spell slot.
9 Phantasmal Force
A level two spell, Phantasmal Force is one of only two damaging illusion spells. It is a ranged spell attack, requiring an intelligence saving throw from the target. If the target fails its save each turn and the caster maintains concentration, the target will receive damage each turn.
While the damage dealt is initially psychic, players have some control over what damage type the target takes, as the damage for Phantasmal Force will change to whatever damage type the target last received. Its primary drawback is that the damage output is delayed until the creature's turn, providing plenty of opportunity for casters to lose concentration.
8 Silence
Silence is the bane of any caster, but players can use that same power against enemy casters! Anyone within silence's large area of effect will be silenced and unable to cast most spells.
While this is its primary function, an interesting side use is that creatures within the area are also immune to thunder damage. The level two spell is concentration but lasts for a whopping one hundred turns, so it will pretty much remain active until the caster loses concentration.
7 Hypnotic Pattern
At a third level spell slot, Hypnotic Pattern is a very strong debilitating spell with a large area of effect. Any creature that fails its wisdom saving throw against 
Hypnotic Pattern will be unable to move or take actions, bonus actions, or reactions.
A very powerful spell for a fairly low level, the main drawbacks to Hypnotic Pattern are that it only lasts two turns, assuming the caster can maintain concentration and that affected creatures can be brought out of the hypnosis by taking damage and being helped or shoved. Furthermore, the large radius makes it hard to exclude allies from the spell's effect.
6 Fear
Another illusion spell that extends in a cone from the caster, Fear is a third level spell that forces anyone caught in the cone to make a Wisdom saving throw. Should they fail, targets will drop what they are holding and become Fearful of the caster, incapacitating them for three turns, as long as the caster maintains concentration.
Even if targets recover from the Fearful state, dropping their weapon can render them useless for at least another turn. It's a handy spell for dealing with large groups of enemies.
5 Blur
While it is only a second level spell, Blur is a very useful one. It lasts for ten turns, as long as casters maintain concentration, although this is a lot easier given that Blur causes anyone attacking the caster to do so with disadvantage.
Blur is almost foolproof, but creatures that don't use sight to attack or who can see through illusions will not suffer the disadvantage of Blur. Furthermore, it can feel like a waste if casters are hit and lose concentration on Blur almost immediately. It is a risk worth taking for a strong attack-mitigating spell, though.
4 Invisibility
Invisibility is guaranteed to be a favored illusion spell to cast on rogues since invisible characters attack with advantage. Interactions break a character out of invisibility, but it can be an essential spell to gain an early upper hand in combat.
It is also useful for general stealth, although it should be used in turn-based mode, as the ten turn duration is short in real-time. The second level spell is available to the duergar race once per combat at fifth level. Duergar invisibility is also unlimited outside of combat.