Lashknife 

Enchantment — Aura
If you control a Plains, you may tap an untapped creature you control rather than pay this spell's mana cost.
Enchant creature
Enchanted creature has first strike.
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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.
Orim's Cure 100%
$0.14#29485
"If you control a Plains, you may tap an untapped creature you control rather than pay this spell's mana cost."
Angelic Favor 100%
$0.24#24107
"If you control a Plains, you may tap an untapped creature you control rather than pay this spell's mana cost."
Ramosian Rally 100%
$0.30#26549
"If you control a Plains, you may tap an untapped creature you control rather than pay this spell's mana cost."
Sivvi's Valor 100%
$0.36#20626
"If you control a Plains, you may tap an untapped creature you control rather than pay this spell's mana cost."
Swallow Whole 86%
$0.24#19754
"As an additional cost to cast this spell, tap an untapped creature you control."