Memory Crystal 
Artifact
$2.14 #23969 0.60 28.2 years
Buyback costs cost 
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Cards similar to Memory Crystal 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.
Stone Calendar89%
$14.67↑#202700.48↓32.1 years↑
"Spells you cast cost 
less to cast."
less to cast."
Helm of Awakening86%
$1.51↓#1903↑0.36↓29.6 years↑
"Spells cost less to cast."
less to cast."
Spellwild Ouphe84%
$0.32↓#16327↑0.29↓19.3 years↓
"Spells that target this creature cost less to cast."
less to cast."
Emerald Medallion82%
$4.07↑#586↑0.20↓28.9 years
"Green spells you cast cost less to cast."
less to cast."
Pearl Medallion82%
$5.55↑#454↑0.23↓28.9 years
"White spells you cast cost less to cast."
less to cast."
Sapphire Medallion81%
$7.39↑#365↑0.30↓28.9 years
"Blue spells you cast cost less to cast."
less to cast."
Naiad of Hidden Coves80%
$0.22↓#10368↑0.526.6 years↓
"During turns other than yours, spells you cast cost less to cast."
less to cast."
Jet Medallion80%
$12.06↑#278↑0.22↓28.9 years
"Black spells you cast cost less to cast."
less to cast."
Hardened Berserker80%
$0.03↓#240460.06↓11.4 years↓
"Whenever this creature attacks, the next spell you cast this turn costs less to cast."
less to cast."
Geyser Drake80%
$0.15↓#8498↑0.43↓2.4 years↓
"During turns other than yours, spells you cast cost less to cast."
less to cast."
Ruby Medallion80%
$13.06↑#291↑0.28↓28.9 years
"Red spells you cast cost less to cast."
less to cast."
Uthros Psionicist78%
$0.31↓#9825↑0.23↓1.1 years↓
"The second spell you cast each turn costs less to cast."
less to cast."
Raging Battle Mouse78%
$0.24↓#12241↑0.06↓3.0 years↓
"The second spell you cast each turn costs less to cast."
less to cast."
Highspire Bell-Ringer78%
$0.17↓#10995↑0.17↓1.4 years↓
"The second spell you cast each turn costs less to cast."
less to cast."
Urza's Filter76%
$4.79↑#14485↑0.35↓25.9 years↓
"Multicolored spells cost less to cast."
less to cast."
Killian, Ink Duelist76%
$0.29↓#3392↑0.39↓5.4 years↓
"Spells you cast that target a creature cost less to cast."
less to cast."
Herald of Kozilek74%
$0.37↓#6236↑0.07↓10.9 years↓
"Colorless spells you cast cost less to cast."
less to cast."
Cheering Fanatic74%
$0.14↓#198780.36↓8.2 years↓
"Whenever this creature attacks, choose a card name. Spells with the chosen name cost less to cast this turn."
less to cast this turn."
Accursed Witch // Infectious Curse73%
$0.26↓#10650↑0.43↓10.4 years↓
"Spells your opponents cast that target this creature cost less to cast."
less to cast."
Planar Gate72%
$77.60↑#213200.6832.3 years↑
"Creature spells you cast cost less to cast."
less to cast."