I know it would seriously annoy me. When there’s a typographical error (or incorrect plural or whatever), the eye is drawn to it more than to other words, making it stand out and potentially breaking the reader’s train of thought if it’s striking enough.
The easiest way to implement this would likely be to make a table of “irregular” plurals (as in nouns which aren’t second declension masculine in Latin), such as octopus -> octopodes (Greek, but rapidly falling from common use), lusus -> lusus (rare Latin fourth declension) and circus -> circuses (common Latin fourth declension). If the word is not listed in the table, remove the -us and replace it with -i. But there are enough different Greek and Latin plurals in English (such as -ion to -ia, -um to -a, -a to -ae) that you could make “add an -es” the default rule and store the others as exceptions. Either way, you’ll need a table of exceptions.
Alternately, since I doubt these names will truly be procedurally generated in your game (i.e. octopodes only appear if you write code for them, the word isn’t picked randomly by the engine), you could set the printed plural name of a prop to “succubi” when you set its printed name to “succubus” and so on, hard-coding each case when it is used.