Mirror Image

Level 2 Illusion spell available to Sorcerers, Warlocks, and Wizards. Three illusory duplicates of you, each worth +3 Armour Class. Ten turns, no Concentration. It is the best defensive spell a squishy caster can put on themselves and it is not close.

Spell description: Create 3 illusory duplicates of yourself that distract attackers. Each duplicate increases your Armour Class by 3. Whenever you successfully evade an attack, one of the duplicates disappears.

Spell properties

• Range: Self
• Duration: 10 turns
• Conditions applied: Three duplicates, each granting +3 Armour Class. A duplicate is destroyed each time an attack misses you.
• Cost: Action + Spell Slot
• Recharge: Per action

Spell upcasting

Casting Mirror Image at higher levels provides no additional benefits.

How to obtain Mirror Image

• Sorcerer, Warlock, Wizard at Class level 3

Source items: Shelter of Athkatla, Scroll of Mirror Image

When to cast Mirror Image

+9 Armour Class is an absurd number. A Wizard sitting on 13 goes to 22, which is better than a Paladin in full plate, and most of Act 1 and Act 2 simply cannot roll that. The duplicates only pop when an attack misses, so a good Mirror Image can eat an entire enemy turn and still leave you with images to spare.

The bit people miss: it is not Concentration. That is what makes it exceptional. Your Wizard can be holding Web or Hold Person and still be wrapped in +9 AC. Nothing else at this level competes.

Cast it before the fight, not during. Ten turns covers a whole encounter if you put it up on the approach, and spending your Action on defence once combat is live is a turn where you dealt no damage.

Stack it with Blur if you like. Blur imposes Disadvantage, Mirror Image raises AC, and the two multiply rather than overlap. A caster running both is effectively unhittable by anything ordinary. Blur is Concentration though, so that is your control spell gone.