Okay here it is-if you have a {Corpsejack Menace} on the battlefield and you cast a {Mikaeus the Lunarch} (XW) for say 5 it should enter with 4 counters on it, does Corpsejack Menace double that or does it enter with 4 still. My friend says it doubles it but I say because it already has the counters when it enters the battlefield, it doesn't. Also if it entered and than got the counters wouldn't it die the moment you cast it because it would be a 0/0 for that split second?
Creatures like Mikaeus enter with the counters on them. They are not counted as being 0/0. {Corpsejack Menace} will affect creatures that enter with +1/+1 counters, as stated in its ruling from Gatherer:
10/1/2012 If a creature you control would enter the battlefield with a number of +1/+1 counters on it, it enters with twice that many instead.
Also, I modified your post to link the cards. You can use curly brackets (quote my post to see) to do so.
Thanks