This will get a bit pedantic but bear with me because I think it does have an effect on reader interpretation. It's not the most pressing issue because it concerns a whopping two whole articles, but I still think it's worth discussing.
On Mettaton's page his pronouns are listed as
he/him (currently)
they/them (ghost form)
currently Mad Mew Mew's page has her pronouns listed as
she/her
Given their unique status as characters who have transitioned either before/during the game, I think it should be sorted out whether to list their old pronouns at all, and to keep it consistent between the two articles.
My first point is that if a character's old pronouns are to be listed, it should not be written as (ghost form) but instead (former). "ghost form" implies that if these characters were to momentarily lose their bodies, their pronouns would revert back to they/them rather than she or he. I think this is inaccurate both to the in-game characters as well as how pronouns function in real life - they correspond to a person's sense of self & expression rather than what body they inhabit. Were Mettaton to somehow lose his body, he would still be a "he". Saying "former" makes that clearer.
My second point is to argue for not including former pronouns. This might be tricky, because on one hand a wiki is meant to be informative, and this provides information about their pasts. On the other hand, sometimes people will take "former" pronouns to mean a person should be referred to their old pronouns when speaking about their past, rather than using their current pronouns (for instance, when referring to a mtf woman, saying "when he was a boy".) This isn't considered respectful or accurate by most trans people, and is usually confusing. Not to mention, both these characters' pasts as ghosts is already provided in the body of the article anyways.
Also, I could argue the pronouns section of the infobox should only refer to current pronouns just to make it crystal clear what characters actually go by. If the purpose of the pronouns section is to clear up misconceptions about what pronouns characters use, then it should only be what they actually use/what they want to use. This better prevents confusion.
Personally I am much more in favor of only listing current pronouns for those reasons. I want to ask for a discussion rather than just going in there and making a decision by myself. I ask that anyone not familiar with trans issues and grammar to not chime in, especially if it is to argue it doesn't matter or that these characters have nothing to do with trans issues. Good faith discussion only.
Edit: there has been discussion in the discord server about including they/them (former*) with a note that links to a history section that should be added to the article anyways. This would make it clear what he currently uses, and what his past was without introducing ambiguity.