Now that I've seen the first episode of Mhom Ped Sawan, sadly without subtitles because I was too impatient to wait, I can see that this costume is representing Kaeo, the Horse-Faced girl, a very well known Thai legend.

I thought at first, from pictures alone, that Khwan might be playing the golden deer from the Ramakien but you can see in the dance that Kaeo is trying to impress the prince and he is not having it, (because of her aforementioned horse face.)

Personally I think Khwan makes a very pretty pony 🐎

Khwan's dad seems really proud of him which is very cute but that actor played Phraya Bodisorn in ManSuang so I still have a lot of mistrust for him 😂