When the Room spell resolves, the corresponding door becomes unlocked as the Room enters
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For starters, getting to potentially affect all artifacts in play is a big deal
Heartflame Duelist: Discover 3 sees Heartflame Duelist as a 2-mana spell, so you may cast that creature
It can be a payoff for a go wide deck, but often those decks are not interested in playing big creatures, thus I expect the Sheriff to be a card that ends up wheeling a lot
And that hasnt ended, we just flavor stuff after planeswalkers (Jace's Erasure, Liliana's Specter, Chandra's Ignition) or still after legendary creatures (Ezuri's Predation, Daxos's Torment, Kalemne's Captain, Gisa's Bidding, Geralf's Masterpiece, Oona's Grace, etc)