[First things first: names. In Chrono Trigger, many of the character names — especially those of NPCs — differ wildly between the original Japanese and the English localization. The character I’ll be talking about is called Mayonne in Japanese and Flea in English. I’ll be referring to them as Flea, both because I’m writing in English and that’s the name most English-speaking people would be familiar with, and because the screencaps I’m using are from the localization and refer to them as Flea. Accordingly, I’ll be using English names and terminology from the DS port, since that’s the version I played.]

Flea is a miniboss in the legendary RPG Chrono Trigger and something of a minor genderqueer icon. They’re a magician and a shapeshifter, appearing in the form of a young woman — their mannerisms and speech patterns are also quite feminine, and they refer to themself as “atai,” a corruption of the feminine first-person pronoun “atashi.” However, when party member Frog refers to them as a woman,¹ Flea is quite offended, saying they’re a man and shocking the party. They then clarify that they don’t really care either way, and what matters to them is strength. There’s also an item called Flea’s Bustier (Mayonne’s Bra in Japanese) that you can get from them, which can be equipped by both male and female party members, unlike most other implicitly gendered equipment.
So yes, there is a lot of gender happening here. As a shapeshifter, Flea can presumably present however they choose — when we first see them, it’s as a bat that follows the party around. If they look like a woman, it’s because they want to look like a woman. They certainly don’t seem to identify as one, though — while their birth sex is a mystery, they clearly prefer to be seen as a man or nonbinary, and definitely not as a woman, despite choosing to present as one. “Transfeminine nonbinary” probably gets us closest to existing identity categories, though it’s complicated by the fact that they’re (apparently) female-bodied.

Flea doesn’t have much screentime and isn’t much discussed — most of what we see is the party being shocked at the notion of someone gender non-conforming. That, plus Flea’s unusual and contradictory gender presentation, makes me seriously doubt the makers of Chrono Trigger were acting in good faith. It’s the same tired trope of genderqueer and gender non-conforming people being the butt of jokes. I couldn’t say that Flea is good representation.
That said, if you completely put aside creator intention and the reactions of other characters, looking just at Flea themself… Well, they’re kind of a gender, aren’t they? Enjoying female presentation without wanting to be seen as cis is a very real thing, especially for AFAB people. There’s something fun in the contradictions of their gender presentation as well — choosing a female body but referring to yourself as a man is a good way to make sure you’ll be seen as both and neither, which is the whole point.
Basically, I kind of love Flea. They’re playing tenth-dimensional gender chess and no one who created them — let alone the other characters — can keep up. They say what they care about is power, and their gender is unbelievably powerful. No, they’re probably not good rep. But they’re certainly iconic.

¹ – It’s unclear whether or not Frog would be aware he’s misgendering Flea here — they’ve met and fought before on at least one occasion, but it’s possible it just didn’t come up.