Maelstrom Nexus {W}{U}{B}{R}{G}
Enchantment
The first spell you cast each turn has cascade. (When you cast your first spell, exile cards from the top of your library until you exile a nonland card that costs less. You may cast it without paying its mana cost. Put the exiled cards on the bottom in a random order.)
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Cards that do something similar expected a card that isn't here?
Reports become test cases the matcher is graded against before an update ships. Delvefall isn't a chatbot guessing, it compares the printed rules text of every card with plain math, and examples like yours decide which differences should count.
Rain of Riches 84%
$1.18#1589
"The first spell you cast each turn that mana from a Treasure was spent to cast has cascade."