In Dark Souls, which boss drops the Soul of the Moonlight Butterfly?

In Dark Souls, the Moonlight Butterfly drops the Soul of the Moonlight Butterfly when defeated.

The boss is fought in a narrow bridge-like arena in Darkroot Garden. It stays airborne for much of the encounter and attacks with magical projectiles, so characters built for melee combat must often wait for it to approach the platform. Ranged attacks and magic can damage it while it remains in the air.

The soul can be consumed for souls or traded with a blacksmith to create a special weapon. The Giant Blacksmith in Anor Londo can use it to forge the Crystal Ring Shield, while the soul can also be exchanged for the Moonlight Butterfly Horn through the relevant weapon-upgrade process.

The boss’s name and soul name are nearly identical, which makes this fact straightforward but easy to mix up with Seath’s Moonlight Greatsword. Seath does not drop the Moonlight Butterfly’s soul.