The folowing situation occurs. Is Erebos coming into play tapped or not?

My opponent controls 2 Lifebane Zombie, I control Imposign Sovereign.

My opponent casts Erebos. Does it enter the battlefield tapped or not?

It enters the battlefield untapped.

As a permanent enters the battlefield, you have to determine which replacement effects affect it. For this, you look at how the permanent would look onto the battlefield and take into account:
1. continuous effects from sources that are already on the battlefield,
2. replacement effects generated by the new permanent that affect it specifically

While doing this the permanent isn't on the battlefield yet, so it can't influence the game state as you are evaluating this. In particular, your devotion to black is 4 while you are looking at the game state, so Erebos would not be a creature on the battlefield. In other words, you fix every variable and then consider how the permanent looks on the battlefield, so you evaluate the ability “as long as your devotion to black is less than five, Erebos isn't a creature” in the current context where your devotion is 4. It has nothing to do with what Erebos looks like after it enters the battlefield.

Daniel Kitachewsky
L3, Paris, France
Rules NetRep