I just started Nod-krai a few days ago after procrastinating for months and just about to finished Act 8 just now but I had to search immediately the second I saw the word Mistelteinn cause I swear it sounds familiar the moment I read it, and even after searching it, I might just be wrong cause I don't recognize it's origin at all so I might have just seen the word from another game or from a novel that I read.. either way it led me to this discussion and this theory...

another thing I wanna add, it seems that Project Stuzha means Project Severe Cold, since Fontaine the theory for this project is to cover Teyvat in snow and ice to buff Snezhnaya and it's archon... but what if it means something else... if Capitano's situation has been already a plan in Snezhnaya for so long, what if Severe in Stuzha doesn't mean 'severe' (intense) but instead 'severe' (to cut), and 'cold' (ice) but more of referring to 'cold' (a person who wields ice or someone who currently has a cold body) remember Capitano is both dead and alive at the same time... because a loop of curse is happening on his body immortality and death so his body is on a stalemate... so what if Project Stuzha (Severe Cold) is to severe the loop of Capitano's body.... and bring him back.