Creatures opponents control will be exiled if they would die for any reason that turn, not just if they die by being reduced to 0 or less toughness by Malicious Eclipse.

While the -2/-2 applies only to creatures that are on the battlefield as Malicious Eclipse resolves, the replacement effect applies to all creatures opponents control that turn, including ones that enter the battlefield after Malicious Eclipse resolves, noncreatures that become creatures after Malicious Eclipse resolves, and creatures that become controlled by opponents after Malicious Eclipse resolves.