So why did the grey child say in page 2738 that the Hallowman does not understand the bigger picture?
Just what could possibly be worse than this?
Well, magic opens up a few possibilities, but I do not want to think about it.

Oh all right, just what we needed folks, another psycho who wants to torture the entire planet in a artistic and experimental way!, problem is... that i think we have just too much of people like this in the world, and that is excluding the 3 most wanted psychos that are already doing and excellent job on that matter XD (man i LOVE this comic).

Nice

Noel is smart enough to ham it up with nightmares in order to fool or appease them, as clearly evident by Daddy. So the fact that Noel is willing to contradict or argue with Hallowman tells me he sees an apparent benefit to distracting him with conversation.

Or maybe he's not really feeling friendly this evening. It's been a long day.

Keep him monologuing, Noel!

Hallowman is in a recruiting mood tonight. As long as Noah stays boring he has a chance at reaching Chernyl.

@Brownie : The Grey child said that Hallowman doesn't know of Noah's power and the wishes it can grant. so indeed the Hallowman doesn't know the full picture.

Since we dont know what the first wish is but that Noah had been warned not to tell it to others "for his own sake", it is a possibility the outcome of such a wish would be judged harshly.

The Hallowman seems perturbated, he lost letters in that last speech bubble: INSIGN(i)FICANT and POPULAT(i)ON. Would that be the effect of off-screen Noah visiting his mind?

@Strannik

The way the grey child referred to it in the conversation made me think it was a general disagreement over how terrible the world should be.
It makes more sense if it is about Noahs power specifically.
Though I am suprised the wish can have such a large scale effect when the previous ones were rather restricted. I guess it really comes down to how Noah phrases it.

Since we're all talking about the Grey Child saying Hallowman can't see the bigger picture, I 'll throw my hat on the ring.
See, the way Hallowman and every other nightmare, save the Grey Child it seems, go about their business makes them utterly horrifying. In fact, they're actively horrifying by design, going out of their way to bring as much suffering as possible to as many people as possible in as thorough, fast and far reaching way as possible, and in that regard, Hallowman might just have every other nightmare beat.
Here's the thing though, if he succeeds, he'll have an absolutely enormous number of people horrified of him.
And every single one of those people are gonna want to stop him.
Most people obviously aren't gonna be able to do anything about him, or most other nightmares for that matter.
But what the Hallowman is doing is gonna paint a target on himself, every other nightmare out the and, most importantly, every nightmare's source and greatest weakness:
Chernyl.
And out of all those people, only one, only a single one, has to succeed in taking her out for this entire nightmare to end. At that point, you have to ask yourself, is it impossible for anyone to succeed or is it impossible for everyone to fail, not to mention, unless they have some way of granting Chernyl immortality, she's also subject to dying of old age.
Chances are, the Grey Child realizes this. It is a nightmare itself afterall, I don't think it's exempt from the same primal urges every other nightmare has. It's also not immune to every nightmare's aforementioned greatest weakness. In all likelihood, it intends on playing a long, subtle game. Slowly and carefully manipulating events to turn the world into an increasingly terrifying place, with no one the wiser as to WHY it's becoming worse and worse.
It likely won't even dirty its hands directly

So wait, if the Hallowman can't get out of Chernyl's head and into the wider world to terrorize as he pleases, can Noah rules-lawyer this into a free wish once they deal with the whole nightmare situation? "But DM, the Hallowman said he couldn't get out of Chernyl's head, so clearly I was inside of her mindscape that whole time! I should get a wish!"

Do we really know anything about how Noah's "Wishes" work besides them being powerful in some way? There's some implication they work through the Ciel, but that's a big unknown too.

@megahellreaper

Who says the Grey Child is for sure a nightmare, though?

Grey Child has (very hard to see) horns like Ceil so they're probably a pandemonium spirit, possibly Chernyl's but they also could be a local unbound spirit that was able to manifest because of the magic saturating Haven.

I wouldn't be surprised if the Grey Child turns out to be Chernyl's equivalent of Ciel. Or perhaps, Minori.

The big picture? Something to do with Tobi perhaps? There's more to destruction than random slaughter after all...

I do hope the dead kid overheard the part about the Hallowman having clawed his way out of Chernyl's head: It sounds like the dreamscape should be monster free... new creations aside.

Guys...
Guys please...
Hallowman doesn't see a Big Picture because at the end of the day. He is exactly the same as other Nightmares.
He just wants to murder and torture, sure he is more ambitious about it and wants to torture the Entire World. But he lacks any aspiration to be anything more then just a strong Nightmare.