Serenade

 is a power skill which summons a friendly flying sword. It is exclusively obtained from the Fatal Falls DLC.

Location
In the Fractured Shrines there is an island that can be reached by platforming over invisible platforms. The rain splashes reveal their location. After that there is a small gauntlet of traps that leads to a temple blocked by three layers of breakable floor that requires the to get inside. In the building there is a Stone Warden guarding a door which leads to a unique treasure room with a vault inside. By opening the vault you free Serenade, which will force theirself into a skillslot. The blueprint itself goes in your inventory and still needs to be delivered to the The Collector.