Drain Power 
Sorcery
$3.17 #16498 0.80 33.1 years
Target player activates a mana ability of each land they control. Then that player loses all unspent mana and you add the mana lost this way.
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Cards similar to Drain Power 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.
Piracy78%
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"Until end of turn, you may tap lands you don't control for mana. Spend this mana only to cast spells."
Pygmy Hippo76%
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"Whenever this creature attacks and isn't blocked, you may have defending player activate a mana ability of each land they control and lose all unspent mana. If you do, this creature assigns no combat damage this turn and at the beginning of your next main phase this turn, you add an amount of 
equal to the amount of mana that player lost this way."
equal to the amount of mana that player lost this way."
Mana Short76%
$0.39↓#154921.02↑33.1 years
"Tap all lands target player controls and that player loses all unspent mana."