Wondrous Item, Rare (requires attunement by a ranger or druid)
This finely crafted silver ring has a swarm of crows engraved on the outside.
This ring has five charges, you can use a bonus action to expend up to as many charges are remaining. You summon a swarm of fey that appear as birds for a round for each charge used. All charges are restored at dawn.
Once summoned, you issue a verbal command and the birds swarm a creature of large size or smaller. You can target a different creature (or the same) at the start of your next turn.
That creature must make a dexterity saving throw against your spellcasting DC at the start of its turn. On a fail, it has the effects of the Slow spell until the start of its next turn.
The swarm cannot be damaged, but may be dispelled.