Moustache Mask is one of the two skins released in the Season 4 (Carnival) event. It could be acquired for a limited time from mid February to early March 2020.
Moustache Mask could be acquired by collecting 40 tokens and by purchasing a Golden Pass for $4.99 during the event period. There may be few opportunities to acquire this skin in the future.
Details of this skin may vary depending on location, platform or time.