Floodgate 

Creature — Wall
Defender
When this creature has flying, sacrifice it.
When this creature leaves the battlefield, it deals damage to each nonblue creature without flying equal to half the number of Islands you control, rounded down.
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Cards that do something similar expected a card that isn't here?
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Gustrider Exuberant 91%
$0.11#29604
"Sacrifice this creature: Creatures you control with power 5 or greater gain flying until end of turn."
Shard Phoenix 88%
#19563
"Sacrifice this creature: It deals 2 damage to each creature without flying."
Burdened Aerialist 85%
$0.27#16873
"Whenever you sacrifice a token, this creature gains flying until end of turn."
Kill-Zone Acrobat 84%
$0.05#29174
"Whenever this creature attacks, you may sacrifice another creature or artifact. If you do, this creature gains flying until end of turn."
Aerie Ouphes 82%
$0.22#17045
"Sacrifice this creature: It deals damage equal to its power to target creature with flying."