Herald's Horn 
Artifact
$1.97 #150 0.21 9.0 years
As this artifact enters, choose a creature type.
Creature spells you cast of the chosen type cost 
less to cast.
less to cast.At the beginning of your upkeep, look at the top card of your library. If it's a creature card of the chosen type, you may reveal it and put it into your hand.
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Cards similar to Herald's Horn 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.
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"Creature spells of the chosen type cost 
less to cast."
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"As this enchantment enters, choose a creature type."
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"As this artifact enters, choose a creature type."
Marauding Raptor82%
$0.91↓#3000↓0.187.2 years↓
"Creature spells you cast cost less to cast."
less to cast."
Mirror of the Forebears82%
$1.63↓#10360↓0.53↑9.0 years
"As this artifact enters, choose a creature type."
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$2.62↑#1076↓0.47↑18.6 years↑
"As this artifact enters, choose a creature type."
Rally the Ranks82%
$0.36↓#4621↓0.145.6 years↓
"As this enchantment enters, choose a creature type."
Heartless Summoning82%
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"Creature spells you cast cost less to cast."
less to cast."
Adaptive Automaton81%
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"As this creature enters, choose a creature type."
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"As this artifact enters, choose a creature type."
Shared Triumph80%
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"As this enchantment enters, choose a creature type."
Obelisk of Urd80%
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"As this artifact enters, choose a creature type."
Kindred Discovery80%
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"As this enchantment enters, choose a creature type."
Radiant Destiny80%
$0.34↓#5541↓0.09↓8.6 years
"As this enchantment enters, choose a creature type."