Nightmare Lash 
Artifact — Equipment
$6.59 #11020 0.35 22.9 years
Equipped creature gets +1/+1 for each Swamp you control.
Equip—Pay 3 life. (Pay 3 life: Attach to target creature you control. Equip only as a sorcery.)
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Cards similar to Nightmare Lash 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.
Lashwrithe85%
$0.72↓#8092↑0.2515.3 years↓
"Equipped creature gets +1/+1 for each Swamp you control."
Blackblade Reforged84%
$2.69↓#349↑0.368.4 years↓
"Equipped creature gets +1/+1 for each land you control."
Hand of Vecna78%
$0.36↓#96280.00↓5.1 years↓
"Equip—Pay 1 life for each card in your hand."
+1 more matching line
Sigil of Distinction76%
$1.86↓#14123↓0.3817.9 years↓
"Equipped creature gets +1/+1 for each charge counter on this Equipment."
Staff of Titania75%
$5.23↓#4334↑0.403.8 years↓
"Equipped creature gets +X/+X, where X is the number of Forests you control."
Sima Yi, Wei Field Marshal74%
$30.02↑#28337↓0.3827.3 years↑
"this card's power is equal to the number of Swamps you control."
Dakmor Sorceress74%
$0.30↓#24131↓0.3328.2 years↑
"this card's power is equal to the number of Swamps you control."
Mire Kavu74%
$0.06↓#30957↓0.10↓25.6 years↑
"This creature gets +1/+1 as long as you control a Swamp."
Squelching Leeches72%
$0.12↓#18084↓0.50↑12.4 years↓
"this card's power and toughness are each equal to the number of Swamps you control."
Nightmare72%
$0.15↓#14070↓0.3133.1 years↑
"this card's power and toughness are each equal to the number of Swamps you control."
Gavel of the Righteous72%
$0.27↓#5260↑0.284.4 years↓
"Equipped creature gets +1/+1 for each counter on this Equipment."
Demonmail Hauberk70%
$0.19↓#14627↓0.3214.9 years↓
"Equipped creature gets +4/+2."
Veteran's Powerblade70%
$0.11↓#24575↓0.00↓3.8 years↓
"Equipped creature gets +2/+0."
+1 more matching line
Granite Grip70%
$0.12↓#14597↓0.3827.6 years↑
"Enchanted creature gets +1/+0 for each Mountain you control."