The Lunar Whale 

Legendary Artifact — Vehicle
Flying
You may look at the top card of your library any time.
As long as The Lunar Whale attacked this turn, you may play the top card of your library.
Crew 1
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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.
Gwenom, Remorseless 86%
$4.47#3139
"Whenever this card attacks, until end of turn, you may look at the top card of your library any time and you may play cards from the top of your library. If you cast a spell this way, pay life equal to its mana value rather than pay its mana cost."
Yennett, Cryptic Sovereign 85%
$0.35#10884
"Whenever this card attacks, reveal the top card of your library. You may cast it without paying its mana cost if its mana value is odd. If you don't cast it, draw a card."
Sapling of Colfenor 84%
$7.08#6640
"Whenever this card attacks, reveal the top card of your library. If it's a creature card, you gain life equal to that card's toughness, lose life equal to its power, then put it into your hand."
Hans Eriksson 83%
$0.13#17784
"Whenever this card attacks, reveal the top card of your library. If it's a creature card, put it onto the battlefield tapped and attacking defending player or a planeswalker they control. Otherwise, put that card into your hand. When you put a creature card onto the battlefield this way, it fights this card."
Rulik Mons, Warren Chief 82%
$0.17#12851
"Whenever this card attacks, look at the top card of your library. If it's a land card, you may put it onto the battlefield tapped. If you didn't put a card onto the battlefield this way, create a 1/1 red Goblin creature token."