Bats

Bats are a species of tiny beast common in Barovia. They are also well known to the party from their previous adventures in Faerûn and the Feywild, though of course bats are less commonplace in some parts of Faerûn, and considerably stranger in the Feywild.
It is a mark of Strahd's evil that he's chosen bats as minions, because bats are adorable and should not be associated with such a gnarly dude.