Possibly related: Hubert Schölnast's answer here.
In the German and English versions of the same game I ran across:
"Dass du mich überhaupt siehst, so wie du in andere Richtungen schaust, damit dich ja niemand beobachtet."
"Surprised you saw me, the way you keep looking every other direction to make sure no one's watching."
The English version is missing a subject and verb in the first clause, but in context it's obvious that it should be "I'm". In the German version it's missing a verb and anything to do with being surprised. So I'm having a hard time figuring out if that's implied by context or it's a typographical error of some kind. I would have added .., ist überraschend to the end. I realize that both versions are very informal, and ellipses are allowed in such cases, but it seems like the German version goes too far with it.
PS. I found a description of this construction on LEO (section c). The upshot is that exclamatory sentences can take the form of a subordinate clause. They give three examples; the last one is Dass das so teuer geworden ist! -- "It's gotten so expensive!" I think this explains the original sentence, but apparently LEO is still missing a few things.
First, one of HalvarF's comments gives some examples where surprise is not meant, but according to LEO the construction is an expression of Verwunderung/"amazement". Perhaps any exclamatory sentence contains some degree of amazement, so this might not be a contradiction. Also, the original sentence is meant to be more teasing banter than an actual expression of surprise or amazement.
Second, the link given in Carsten S' comments mentions that you can start such a construction with words other than dass, namely wenn, ob, or a question word. I'm already familiar with the wenn case, but I thought it would only be used with the subjunctive: Wenn ich nur fliegen könnte! -- "If only I could fly!" In any case, the answer in the link seems to focus on terminology and syntax rather than meaning, so it's a bit hard to tell what the example sentences mean. (Google Translate doesn't seem to do well with informal/colloquial German.) LEO only gives examples for the question word was and dass.
Anyway, just knowing that it isn't a typo is a big help. Part of the problem is that informal German like this isn't always covered covered well in grammars, especially ones in English; for some reason they only want to teach you how to speak "proper" German.
PPS. Just for my own future reference if nothing else, I wanted to add a couple more relevant links. First, Grammis mentions something about this type of construction here, starting with the paragraph that begins In dieser Ausprägung. There are five or six examples listed there. Second, this paper gives eight examples at the top of page 13. Finally, DWDS gives some example involving dass in it's entry for that word, definition IIa. The main problem I'm having now is that I can't find any sources in English, and while the examples given in German may be self-explanatory for native speakers, I'm not a native speaker their meaning isn't clear to me. Google translate and DeepL get some of the examples, but sometimes they just give a literal translation and, since we're dealing with a figure of speech here, that's not very useful.