Tainted Adversary
Creature — Zombie
Deathtouch
When this creature enters, you may pay 
any number of times. When you pay this cost one or more times, put that many +1/+1 counters on this creature, then create twice that many 2/2 black Zombie creature tokens with decayed. (A creature with decayed can't block. When it attacks, sacrifice it at end of combat.)
Illustrated by
Innistrad: Midnight Hunt#124MythicEnglishLegality
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.”
Decayed does not create any attacking requirements. You may choose not to attack with a creature that has decayed.
Decayed does not grant haste. Creatures with decayed that enter the battlefield during your turn may not attack until your next turn.
Once a creature with decayed attacks, it will be sacrificed at end of combat, even if it no longer has decayed at that time.