Floodtide Serpent {4}{U}
Creature — Serpent
This creature can't attack unless you return an enchantment you control to its owner's hand. (This cost is paid as attackers are declared.)
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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.
Godhunter Octopus 95%
$0.06#27900
"This creature can't attack unless defending player controls an enchantment or an enchanted permanent."
Bloodcrazed Goblin 88%
$0.18#25197
"This creature can't attack unless an opponent has been dealt damage this turn."
Goblin Cohort 88%
$0.24#24308
"This creature can't attack unless you've cast a creature spell this turn."
Mogg Conscripts 88%
#27105
"This creature can't attack unless you've cast a creature spell this turn."
Silburlind Snapper 87%
$0.04#26997
"This creature can't attack unless you've cast a noncreature spell this turn."
Novice Knight 86%
$0.12#23011
"As long as this creature is enchanted or equipped, it can attack as though it didn't have defender."
Orcish Conscripts 86%
#30294
"This creature can't attack unless at least two other creatures attack."
Lambholt Pacifist // Lambholt Butcher 86%
$0.21#23485
"This creature can't attack unless you control a creature with power 4 or greater."
Warden of the Chained 86%
$0.10#27889
"This creature can't attack unless you control another creature with power 4 or greater."
Lurking Green Dragon 85%
$0.21#22222
"This creature can't attack unless defending player controls a creature with flying."
Harbor Serpent 85%
$0.14#20206
"This creature can't attack unless there are five or more Islands on the battlefield."
Lovestruck Beast // Heart's Desire 85%
$0.23#12443
"This creature can't attack unless you control a 1/1 creature."
Mogg Toady 85%
$0.11#30572
"This creature can't attack unless you control more creatures than defending player."
Goblin Goon 85%
$0.35#20282
"This creature can't attack unless you control more creatures than defending player."
Pillar of War 85%
$0.07#30018
"As long as this creature is enchanted, it can attack as though it didn't have defender."
River Serpent 84%
$0.21#18500
"This creature can't attack unless there are five or more cards in your graveyard."
Vantress Gargoyle 84%
$0.32#11501
"This creature can't attack unless defending player has seven or more cards in their graveyard."