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Instant
Counter target spell unless its controller pays 
. Create a 2/2 black Zombie creature token with decayed.
"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)