It doesnt expire during the cleanup step or if the creature you take has its power raised above 3 later
The thing is you can foretell it so its only five mana and it generates two tapped Treasure tokens when it enters the battlefield
Lastly, copy spells have always been nuts when it comes to other copy spells, but Narset's ReversalNarset's Reversal most likely ends with every spell on the table (including Narset's ReversalNarset's Reversal) back in player's hands, and who knows what else
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Common (36) 1 Brainstorm 1 Dark Ritual 1 Deny Reality 1 Commander's Sphere 1 Wayfarer's Bauble 1 Command Tower 1 Dismal Backwater 1 Evolving Wilds 1 Forgotten Cave 1 Path of Ancestry 1 Swiftwater Cliffs 1 Terramorphic Expanse 8 Mountain 8 Swamp 8 Island Uncommon (20) 1 Heralds of Tzeentch 1 Nurgle's Rot 1 Bloodcrusher of Khorne 1 Chaos Terminator Lord 1 Herald of Slaanesh 1 Noise Marine 1 Seeker of Slaanesh 1 The Lost and the Damned 1 Bile Blight 1 Bituminous Blast 1 Assault Suit 1 Sol Ring 1 Talisman of Creativity 1 Talisman of Dominance 1 Talisman of Indulgence 1 Worn Powerstone 1 Barren Moor 1 Crumbling Necropolis 1 Molten Slagheap 1 Temple of the False God Rare (41) 1 Lord of Change 1 Blight Grenade 1 Great Unclean One 1 Mandate of Abaddon 1 Mortarion, Daemon Primarch 1 Nurgle's Conscription 1 Plague Drone 1 Poxwalkers 1 Sloppity Bilepiper 1 Tallyman of Nurgle 1 Venomcrawler 1 Aspiring Champion 1 Bloodthirster 1 Dark Apostle 1 Keeper of Secrets 1 Khrn the Betrayer 1 Knight Rampager 1 Let the Galaxy Burn 1 Blood for the Blood God

It also flickers creatures when you cast your second spell, which we love to see