Cast Fractured Identity by paying {3}{W}{U}, exiling Maskwood Nexus and causing each opponent to create a token copy of it.
Activate Spirit Mirror by paying {0}, destroying target creature an opponent controls, as it will be a Reflection due to the opponent's Maskwood Nexus.
Repeat step 2 as desired.
You may also repeat step 2 whenever a creature enters the battlefield under an opponent's control.

Destroy all creatures opponents control

Destroy each creature that enters the battlefield under an opponent's control

Lock

Maskwood Nexus

Spirit Mirror

Fractured Identity

Activate Amoeboid Changeling's first ability by tapping it, causing any creature an opponent controls to gain all creature types until end of turn.
Activate Spirit Mirror by paying {0}, destroying the opponent's creature.
When the creature dies, Faces of the Past triggers, untapping Amoeboid Changeling.
Repeat.

Amoeboid Changeling

Faces of the Past

Activate Amoeboid Changeling's first ability by tapping it, causing any creature an opponent controls to gain all creature types until end of turn.
Activate Spirit Mirror by paying {0}, destroying the opponent's creature.
The creature dies, triggering Amoeboid Changeling, untapping Amoeboid Changeling.
Repeat.
You may also repeat this loop whenever a creature enters the battlefield under an opponent's control.

Thornbite Staff

Cast Artificial Evolution by paying {U}, changing all instances of "Reflection" on Spirit Mirror to "Bear".
Activate Spirit Mirror by paying {0}, destroying target creature as it is a Bear due to Kudo.
Repeat step 2 as desired.
You may repeat step 2 whenever a creature enters the battlefield under an opponent's control.

Artificial Evolution

Kudo, King Among Bears

Activate Spirit Mirror by paying {0}, targeting any Reflection.
Crackdown Construct triggers, giving itself +1/+1 until end of turn.
Repeat.
Resolve all Spirit Mirror abilities, destroying the targeted Reflection(s).

Combos with "Spirit Mirror"