Arni Brokenbrow (Showcase) [Kaldheim] SV91 then you may cast any

then you may cast any number of spells from among those cards without paying their mana costs

Set: Sword & Shield: Black Star Promos Type: Grass Rarity: Promo Retreat cost: 2

Set: Strixhaven: School of Mages Tokens Type: Token Creature — Inkling Rarity: Common Flying

Set: Celebrations: 25th Anniversary Type: Lightning Rarity: Ultra Rare Retreat cost: Colorless

But it will not halt them long

Arni Brokenbrow (Showcase) [Kaldheim] SV91 then you may cast anySet: Kaldheim Type: Legendary Creature Human Berserker Rarity: Rare Cost: {2}{R} Haste Boast {1}: You may change Arni Brokenbrow's base power to 1 plus the greatest power among other creatures you control until end of turn. (Activate only if this creature attacked this turn and only once each turn.)