Hornet

Journal Description
"Skilled protector of Hallownest's ruins. Wields a needle and thread."

Hunter's comments
"I have seen this nimble little creature. I thought her prey and pounced at her, but with a flash she stabbed me with her flying stinger and darted away. Could she be... a Hunter?"

Greenpath Encounter
Upon defeat in Greenpath, she drops the Mothwing Cloak, which allows the player to dash sideways.

Kingdom's Edge Encounter
Her attacks are similar, but this encounter has her throw spikes as well.

Final Boss (Spoilers ahead)
In the final battle, if you have the Void Heart equipped, she allows the hero to strike the final boss with the Dream Nail, allowing them to fight the Radiance.

If you do not have Void Heart or you hurt The Hollow Knight enough, she falls to the floor and the battle continues. After that, she is sealed with you in The Black Egg.

If you beat the Radiance, she will live, but she sees the hero's mask broken on the floor, suggesting that you die.