Whenever a nontoken creature enters that was cast, Mirror of Life Trapping triggers, exiling that creature.
Whenever a nontoken creature enters that wasn't cast, it is instead exiled due to Containment Priest. This also applies to any creatures that would be put onto the battlefield by Mirror of Life Trapping.

Exile all nontoken creatures that enter the battlefield

Lock

Mirror of Life Trapping

Containment Priest

Cast Priest of Gix by discarding another nonartifact black creature card with mana value two or less.
Containment Construct triggers, causing you to exile the discarded card from your graveyard and allowing you to cast it this turn.
Priest of Gix enters the battlefield, triggering itself and Cloudstone Curio.
Resolve the Priest of Gix trigger, adding {B}{B}{B}.
Holding priority, cast the black creature from exile by paying its mana cost.
The creature enters the battlefield, triggering Cloudstone Curio, returning Priest of Gix from the battlefield to your hand.
Resolve the Cloudstone Curio trigger from step 3, returning the black creature to your hand.
Repeat.

Infinite black mana

Infinite creature ETB

Infinite creature LTB

Infinite storm count

Priest of Gix

Containment Construct

Dream Halls

Cloudstone Curio

Teferi, Mage of Zhalfir

Cast Priest of Urabrask by discarding another nonartifact red creature card with mana value two or less.
Containment Construct triggers, causing you to exile the discarded card from your graveyard and allowing you to cast it this turn.
Priest of Urabrask enters the battlefield, triggering itself and Cloudstone Curio.
Resolve the Priest of Urabrask trigger, adding {R}{R}{R}.
Holding priority, cast the red creature from exile by paying its mana cost.
The creature enters the battlefield, triggering Cloudstone Curio, returning Priest of Urabrask from the battlefield to your hand.
Resolve the Cloudstone Curio trigger from step 3, returning the red creature to your hand.
Repeat.

Infinite red mana

Priest of Urabrask

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