Just like Yisan, the Wanderer Bard, this card acts as the perfect toolbox for any deck with a decent amount of creatures
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
Modern also has more one-mana permanents than usual right now, and a lot more zero-mana permanents than usual
Hes well-known for being a miserable mill commander when built correctly, and hell likely get targeted often
When Conspiracy was being announced, the concept of Will of the Council caught my intrigue
A dash of card draw goes a long way in any of the builds but too much is also a danger