I know some of these sound pretty weird, and that is
because they are pretty literal. I’ll break it down:
yami ni ugomeku mono
yami - darkness (sometimes you can translate this as “night”, because of how we use it figuratively in English)
ni - in / at / on / to (in this case, in, because none of the others really makes much sense; this is a “postposition” much like we have “prepositions” in English)
ugomeku - wriggle (refers to bugs or a buglike wriggling motion; it can thus be extended metaphorically to putting on airs when applied to the nose [a meaning wholly irrelevant here] and to the skulking or loitering of no-goodniks [the meaning I suspect is really implied here])
mono - two common readings here: can refer to a “thing” (strictly physical things) or to “a person” (the usage is a bit like we use the “one” in “one should”). Additionally, since nouns in Japanese don’t have grammatical number, they might be plural, so “things” or “those” are very common translation.
Thus an extremely literal translation could be “those who/that wriggle in the darkness”. But this is an awkwardly verbose phrase when you can use the -er instead of “those who”, and typical Japanese usage does not allow their equivalent of “-er” to be applied to this kind of verb anyway.
This is the sort of thing that gets lost in translation pretty often, because as Shakespeare wrote (in the mouth of an ironically garrulous character), brevity is [...] wit.
Given license to translate more figuratively, I would have definitely gone for something else, like “lurking in the darkness”, or “bump in the night”, or even “nightcrawlers”
For what I have translated Hole in the Heart, it is more literally “[a] hole opened in [the] heart/spirit”. Maybe having the verb in there does not sound redundant in Japanese, but in English it really does. This use of “hole” is a figurative sense, of course, but given that this usage and meaning is basically the same as in English, there isn’t a lot of point translating it some other way. Given a less conservative approach (or a character limit as is often the case in games), “heartbreak” is the obvious idea here.
As for グランドシール, I got it wrong and I blame that on being a drunkpost and getting my info from Internet synopses instead of doing my research the fun-but-takes-hours way (i.e. playing the game)
For some reason, a lot of Japanese usage of the English word “ground” is spelled as if it should be pronounced “grand”. This is largely recognized as incorrect by lexicographers (both my Japanese dictionaries have two definitions for グランド, and the “ground” definition redirects the reader to グラウンド; unlike most incorrect or colloquial pronunciations, great care has been taken in both to make グラウンド the canonical reading with グランド permitted). However, terms that are in common use are hard to fight like that. If you see the word グランド in a video game, you have to try and figure out whether they meant “grand” or “ground”, which isn’t usually hard, just a little frustrating as a speaker of English.
Perhaps I am writing a whole lot about nothing here, but these are the kinds of issues we worry about in translation, so I hope it has made interesting reading for someone out there, at least.