Mirror Fiend (5e Creature)
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Medium fiend, any neutral alignment
Replication. The mirror fiend can create up to eight duplicates, excluding its original body (detailed below). It can regain all uses of Replication when it dismisses all of its duplicates during a long rest. The mirror fiend will survive if even a single one of its duplicates live. When the mirror fiend takes a long rest while missing its original body, any one of its duplicates can gain full hit points and become a new "original" mirror fiend, while all the other duplicates disappear.
Reflective Skin When the mirror fiend takes damage from a spell or other magical effect, the damage is reduced by 13 (3d8), to a minimum of 0.
Multiattack. The mirror fiend makes three claw attacks.
Duplicate. The mirror fiend creates a duplicate of itself. The duplicate has the same statistics as the original. The duplicate can immediately make a claw attack. Each duplicate has 10 hit points. A duplicate can use the Duplicate action, but the mirror fiend cannot have more than eight duplicates active at once.
Claw. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 6 (1d12 + 3) slashing damage.
The mirror fiend is a tall demon with skin resembling crumbled diamonds. It is capable of duplicating itself to attack multiple foes at once.
A mirror fiend that is separated from all of its duplicates has a CR of 5 instead.