[So, two items of prerequisite, then: that he help her with his abilities when the time comes, and that he harms no one else in this world unless in self-defense.

Again, reasonable. But again, Henry so hates being told what to do. Yet he is cool-headed enough (now, at least) to know that there's little choice in the matter, and that this route--with a strange witch aiding in his desire to return to Hawkins--might actually be favorable for him, in the end.

So, he tilts his head ever so slightly, and smiles again.]

I don't think any of that is unreasonable. But before I accept, do we know what sort of monsters we're talking about? My abilities will be helpful, you're sure?