Amber Prison 
Artifact
$0.31 #23473 0.25 30.0 years
You may choose not to untap this artifact during your untap step.
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Cards similar to Amber Prison 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.
Phyrexian Gremlins90%
$1.06↑#30717↓0.14↓32.6 years↑
"
: Tap target artifact. It doesn't untap during its controller's untap step for as long as this creature remains tapped."
+1 more matching line
Rust Tick88%
$0.21↓#266040.13↓16.1 years↓
"
,
: Tap target artifact. It doesn't untap during its controller's untap step for as long as this creature remains tapped."
+1 more matching line
Entrancing Lyre88%
$0.11↓#234860.186.7 years↓
"You may choose not to untap this artifact during your untap step."
+1 more matching line
Kill Switch87%
$4.04↑#16897↑1.13↑26.7 years↓
"
,
: Tap all other artifacts. They don't untap during their controllers' untap steps for as long as this artifact remains tapped."
Mole Worms85%
$0.18↓#30398↓0.89↑31.4 years↑
"
: Tap target land. It doesn't untap during its controller's untap step for as long as this creature remains tapped."
+1 more matching line
Mana Leech85%
$0.26↓#30404↓0.2528.0 years↓
"
: Tap target land. It doesn't untap during its controller's untap step for as long as this creature remains tapped."
+1 more matching line
Vedalken Certarch84%
$0.09↓#275150.2016.1 years↓
"
: Tap target artifact, creature, or land. Activate only if you control three or more artifacts."
Deserter's Quarters80%
$0.17↓#29809↓0.3212.5 years↓
"
,
: Tap target creature. It doesn't untap during its controller's untap step for as long as this artifact remains tapped."
+1 more matching line
Elder Druid78%
$0.30↓#266210.00↓31.4 years↑
"
,
: You may tap or untap target artifact, creature, or land."
Sand Squid78%
$0.59↑#262240.2727.0 years↓
"
: Tap target creature. That creature doesn't untap during its controller's untap step for as long as this creature remains tapped."
+1 more matching line