There are several unique and event-themed Pokémon for you to encounter while playing Pokémon Go. One of the more unique ones is Umbreon wearing a night scarf, which only appears during the Pokémon Go Fest 2024 event.

Umbreon wearing a night scarf only appears briefly and only for specific encounters. If you want the best chance to catch this Pokémon, purchase a ticket to the Pokémon Go Fest 2024 Global event. It appears at multiple points throughout the event, and primarily on the first day. It could be on the second one, but the chances might not be the best.