It refers to powerful spells, but to me joining random people's dreams is a pretty powerful one. I didn't get at all that Elsa was immediately going to start wielding magic (or even could for that matter). To me the magic in question was always Chloe's, as it's the only magic we knew of.
Also, the game never mentioned that a spell would also be used to locate Chloe. My take on the text was the "tried and true" surprise will create just enough lapse in a person's concentration that they will be momentarily vulnerable (thinking, we haven't spotted her because she is consciously making herself invisible or some such and a loss in concentration will make her partially visible). Either way, I did feel like finding Chloe came a bit late to match this interpretation (As the lapse would occur the split second when they flew or submerged, not significantly later after they had time for sex). Felt more like you just wanted to get the sex scene in first, because after Chloe was noticed, they could hardly go back to ignoring her and having sex to deal with her later.
I see from your elaboration that this is way off the mark. Impossibility and surprise, which seemed like the main points, are actually completely irrelevant. The point is simply that Chloe is supposed to realize that Elsa is actually a powerful witch in her own right. Chloe's to stew on that thought for a bit, while keeping the spell intact (although I feel like there's a pretty good chance that she would actually break the dream connection instantly). Then Elsa wields her second, unmentioned spell and tracks Chloe by strong emotion.
It'd be more clear to me if the script changed from
original wrote:"It's actually not true. According to the book, we can do minor things like go to the beach and make a chair appear. But it takes more powerful spells to allow you do stuff that's really impossible, like breathe under water."
So if we do something impossible...
"Chloe will know that I read the book. I think I'll be able to sense her reaction, which will let me force her out of hiding."
So, what impossible thing are we going to do?
"I'm going to fuck you underwater."
to something more like
edited for content to run in the allotted time wrote:"It's actually not true. According to the book, we can do minor things like go to the beach and make a chair appear. But a dreamer needs to actually cast a spell to do stuff that's really impossible, like breathe under water."
Okay, so no trips to the moon. Wait. Can anybody... Can you cast spells now?
"I always could, but I need to be taught a spell to cast it. Anyway, Chloe's obviously after more power. If she senses me casting a spell of my own, she'll want it. I can detect strong emotions, but if she's hiding behind a spell, I'm not sure her power lust will be enough."
So, you'll do something impossible, but what can we do to push her over the emotional edge?
"I'm going to fuck you underwater."
This was my attempt to only edit some text: no picture, page count or layout, nor plot changes from your original intent (although the lust bit is clearly a minor plot adjustment). Obviously there are other options, including the "you're the only one that doesn't understand and I like my story exactly how it is" option.
Just thought I'd offer some thoughts.