Greetings! Professional Latinist here! I am so happy to see Latin being used in a VN! I noticed that there were some grammatical errors and awkward spots in Kerlno's spell and wanted to offer some suggestions to fix those.
Liquorum compositio, coite, exsolvimini...
-The imperatives here have been attracted into the plural because of liquorum, they though they should be singular to match the vocative compositio. If you want to keep the imperatives in the plural, I recommend changing liquorum compositio to something like liquores commixti. If you want to keep liquorum compositio, then I recommend changing coite to coi and exsolvimini to exsolvere.
ut gelus aeterni quod terras vexant...
-I would recommend using sicut or proinde here instead of ut, just to make things a bit clearer.
-Given the usage of vexant, the relative pronoun should be quae with undae as the antecedent. If you want gelus to be the antecedent, then keep quod and change vexant to vexat.
Este caeli gelidi gemma...
-The imperative has been attracted into the plural again, like in the first sentence. If you use something like liquores commixti, then you can keep este. Otherwise make este singular to make it agree with compositio.
...saussurea involucrata pruinosa.
-This phrase is awkward, literally reading as "frosty/frostily enveloped". I would recommend either making pruinosa a noun for frost or just dropping involucrata.
ut confundamini velut ampla nix penetrabilis estis...
-This phrase reads rather awkwardly, such that it doesn't make a lot of sense in the Latin. I would highly recommend rephrasing this part. An example of such rephrasing could be something like this: ut in essentiam nivis immensae acerbaeque mutemini (plur)/muteris (sing).
-Attracted plural verb again with confundamini.
...ruatis, iubeo!
-Another attracted plural verb with ruatis.
-The verb iubeo does not use indirect command, but instead uses an accusative infinitive construction. If you want to keep the indirect commands as they are, use impero instead.
If you make the following changes, the Latin should become clearer. If you would like stylistic feedback to make the spell match the translated poetic flare, I would be happy to help. Thank you for writing this wonderful work!