Activate Cayth by paying {2} and tapping it, creating a token copy of a creature token you control.
When the creature token enters the battlefield, Mana Echoes triggers, adding {C} for each creature you control that shares a creature type with it.
Activate Staff of Domination's third ability by paying {3}, untapping Cayth.
Activate Staff of Domination's first ability by paying {1}, untapping it.
Repeat.

Infinite creature ETB

Infinite colorless mana

Infinite lifegain triggers

Infinite lifegain

Infinite card draw

Infinite untap of creatures you control

Infinite draw triggers

Infinite mana creatures you control can produce

Infinite proliferate

Infinite copies of creature tokens you control

Cayth, Famed Mechanist

Mana Echoes

Staff of Domination

Activate Cayth by paying {2} and tapping it, creating a token copy of a creature token you control.
When the creature token enters the battlefield, Mana Echoes triggers, adding {C} for each creature you control that shares a creature type with it.
Activate Cayth by paying {3} and untapping it, giving it +2/+2 until end of turn.
Repeat.

Infinitely large creature until end of turn

Umbral Mantle

Activate Cayth by paying {2} and tapping it, creating a token copy of a creature token you control.
When the creature token enters the battlefield, Mana Echoes triggers, adding {C} for each creature you control that shares a creature type with it.
Activate Sword of the Paruns by paying {3}, untapping Cayth.
Repeat.

Sword of the Paruns

Activate Cayth by paying {2} and tapping it, creating a token copy of a creature token you control.
When the creature token enters the battlefield, Mana Echoes triggers, adding {C} for each creature you control that shares a creature type with it.
Activate Singing Bell Strike by paying {6}, untapping Cayth.
Repeat.

Singing Bell Strike

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