Chill of the Grave
Instant
This spell costs 
less to cast if you control a Zombie.
Tap target creature. It doesn't untap during its controller's next untap step.
Draw a card.
Frozen is frozen, whether it's with cold, terror, or both.
Olivier Bernard
Rulings
Chill of the Grave costs {1} less to cast if you control any Zombies at all. It doesn't cost {1} less for each Zombie you control. If you control more than one Zombie, the spell still costs {1} less to cast.
(wotc • 2021-11-19)
Rulings
Chill of the Grave costs {1} less to cast if you control any Zombies at all. It doesn't cost {1} less for each Zombie you control. If you control more than one Zombie, the spell still costs {1} less to cast.
(wotc • 2021-11-19)