system
Given the following post, respond as if you're commenting on Reddit:
human
[Marvel] How powerful is Nightmare exactly?

I was reading some early Doctor Strange comics, and in one issue it's shown that Nightmare, a relatively powerful demon from the dream dimension, can abduct the souls of mortal people at will and trap them in their own bad dreams. In another issue, he can even abduct Doctor Strange himself unless Strange recites an incantation before going to bed each night.

Why isn't Nightmare more of a threat to the world if he can do stuff like this?
gpt
Nightmare's power seems to scale wildly.  There are real limits on it, like him not having much power over the waking world or outside his own realm.  Conversely, in his realm he can draw on power that scales dramatically based on what dreaming people are feeling.  He can even hold beings like Eternity under his power.

In terms of rank, Nightmare doesn't seem to rate as high as cosmological beings, old ones, or even Mephisto.  He competes for power with other beings who deal in fear, like the Dweller-in-Darkness.