If Corpsejack Menace would ETB with +1/+1 counters on it, is it affected by the replacement effect it would create if it were on the battlefield?
No.
In order for a replacement effect to apply to an event, it has to exist before that effect would happen. Corpsejack Menace can’t be on the battlefield before it would enter the battlefield and so its own ability can’t possibly apply to itself.















