Nylea, Blind Obedience

Assume your opponent controls Blind Obedience, your devotion to green is four, and you play Nylea, God of the Hunt. Question: Will it enter the battlefield tapped or not?

Nylea is a creature spell on the stack. (Well, technically speaking an enchantment creature spell, but that's not important here.) Its ability that makes it not be a creature if your devotion to green is too low doesn't come into effect until it's on the battlefield.

In fact, if we look at the whole process of the spell resolving, there isn't a single moment where the effect kicks in and it stops being a creature: As soon as it hits the table, your devotion to green will be five, and thus the ability does nothing. There isn't even a single moment where Nylea isn't a creature.

Because of all the above, the intuition would be that it enters the battlefield tapped. However, that's not so. (Many players will have the intuition that it enters untapped and, while this is the correct answer, might not know the exact reason.)

This is once again a question of how an "enters-the-battlefield replacement effect" works for a resolving permanent spell. What's happening here is this:

As the Nylea spell starts resolving, it will look if any ETB replacement effects will affect it. In this case there's one such effect that may potentially affect it: That of Blind Obedience. Said effect affects artifacts and creatures, and thus what we are looking for is the question: "Is this an artifact or creature when it hits the board?" If the answer is yes, then Blind Obedience's replacement effect will take place, else it won't.

So we "look forward in time" to see how Nylea would look on the battlefield (to see if it's an artifact or a creature there.) There are certain things that are taken into account when doing this. One of those things are abilities on the card that affect the permanent itself (rather than an ability that affects a group of permanents with certain characteristics), and Nylea has such an ability: "As long as your devotion to green is less than five, Nylea isn't a creature."

In other words, we look if Nylea would be a creature on the current battlefield, taking into account that ability. And the answer is: No, it wouldn't be a creature. And the reason for this is that your devotion to green at this moment is four, and thus the ability stops it from being a creature.

This is quite a curious situation. "Devotion" only looks for permanents that are already on the battlefield. It doesn't see this "hypothetical permanent" that we are handling here (for the purposes of determining whether it's a creature or not.) Nylea isn't on the battlefield yet, and thus doesn't change your devotion to green.

Thus the full chain of events is: The Nylea spell starts resolving, we "look forward in time" to see how it would look like on the battlefield, we see that it wouldn't be a creature (because your devotion to green is four), thus Blind Obedience does not affect it, and then it finishes resolving and enters the battlefield untapped as a creature (because now your devotion to green is five.)