Level
2nd
Casting Time
1 Action
Range/Area
Self
Components
V, S
Duration
1 Minute
School
Illusion
Attack/Save
None
Damage/Effect
Deception (...)
Three illusory duplicates of yourself appear in your space. Until the spell ends, the duplicates move with you and mimic your actions, shifting position so it’s impossible to track which image is real.
Each time a creature hits you with an attack roll during the spell’s duration, roll a d6 for each of your remaining duplicates. If any of the d6s rolls a 3 or higher, one of the duplicates is hit instead of you, and the duplicate is destroyed. The duplicates otherwise ignore all other damage and effects. The spell ends when all three duplicates are destroyed.
A creature is unaffected by this spell if it has the Blinded condition, Blindsight, or Truesight.
What happens if you cast it multiple times? If you cast it 2 times would it effectively be roll 6d6 on any 3+ you lose one? Then still have 5 hit buffer?
Unfortunately, it does not work that way. Per the general rules on spellcasting, the same spell cast multiple times on the same target doesn't stack.
Casting it again before the first one ends will effectively extend the duration and "refresh" the number of duplicates you have back to 3 if some were lost, but it doesn't add to the effect of the previous casting.
What if you use Magic Missile?
I think creatures with TremorSense are affected as normal when they attack someone using Mirror Image. (otherwise the designers should've included this in the Unaffected list). The Dungeon Master could rule this as the duplicates have weight/mass...
I think Magic Missile would bypass Mirror Image/strike only the caster & not the duplicates, as Magic Missile does not use an attack roll.
A creature with Tremorsense is affected by the spell RAW.