Thalakos Dreamsower 

Creature — Thalakos Wizard
$0.24 #26053 0.32 28.9 years
Shadow (This creature can block or be blocked by only creatures with shadow.)
You may choose not to untap this creature during your untap step.
Whenever this creature deals damage to an opponent, tap target creature. That creature doesn't untap during its controller's untap step for as long as this creature remains tapped.
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Cards similar to Thalakos Dreamsower 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.
Somnophore96%
$0.46↑#259220.11↓27.9 years
"Whenever this creature deals damage to a player, tap target creature that player controls. That creature doesn't untap during its controller's untap step for as long as this creature remains on the battlefield."
Neko-Te88%
$5.32↑#19108↑0.2421.6 years↓
"Whenever equipped creature deals damage to a creature, tap that creature. That creature doesn't untap during its controller's untap step for as long as this Equipment remains on the battlefield."
Dungeon Geists86%
$0.12↓#18025↑0.21↓14.6 years↓
"When this creature enters, tap target creature an opponent controls. That creature doesn't untap during its controller's untap step for as long as you control this creature."
Sand Squid86%
$0.57↑#258100.4126.9 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
Deserter's Quarters84%
$0.14↓#294800.14↓12.3 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
Ty Lee, Chi Blocker80%
$0.47↑#6825↑0.00↓0.8 years↓
"When this card enters, tap up to one target creature. It doesn't untap during its controller's untap step for as long as you control this card."