Nobody expects a fully committed character to walk into their event. That is precisely why it works.
Costumed characters bring a room to life in a way no amount of decoration can. Ice queens and princesses for children who genuinely believe it, mascots for family days and brand activations, festive characters through December, or something properly strange for a themed party. They stay in character throughout, work the room, run activities where you want them, and pose for every photograph asked of them.
Costumes can be built around your theme, your brand or your event, so the whole thing feels made for you rather than pulled off a shelf.