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Instant
Counter target spell unless its controller pays 
. Create a 2/2 black Zombie creature token with decayed. (It can't block. When it attacks, sacrifice it at end of combat.)
"Works every time! Well, every time they don't explode, anyway." —Barton, stitcher
Campbell White
Rulings
Decayed represents a static ability and a triggered ability. "Decayed" means "This creature can't block" and "When this creature attacks, sacrifice it at end of combat."
(wotc • 2021-09-24)
Decayed does not grant haste. Creatures with decayed that enter the battlefield during your turn may not attack until your next turn.
(wotc • 2021-09-24)
Once a creature with decayed attacks, it will be sacrificed at end of combat, even if it no longer has decayed at that time.
(wotc • 2021-09-24)
You will create a Zombie creature token even if the spell's controller pays {4}.
(wotc • 2021-09-24)
Decayed does not create any attacking requirements. You may choose not to attack with a creature that has decayed.
(wotc • 2021-09-24)
Rulings
Decayed represents a static ability and a triggered ability. "Decayed" means "This creature can't block" and "When this creature attacks, sacrifice it at end of combat."
(wotc • 2021-09-24)
Decayed does not grant haste. Creatures with decayed that enter the battlefield during your turn may not attack until your next turn.
(wotc • 2021-09-24)
Once a creature with decayed attacks, it will be sacrificed at end of combat, even if it no longer has decayed at that time.
(wotc • 2021-09-24)
You will create a Zombie creature token even if the spell's controller pays {4}.
(wotc • 2021-09-24)
Decayed does not create any attacking requirements. You may choose not to attack with a creature that has decayed.
(wotc • 2021-09-24)