Serenade

To get Serenade you need to have unlocked the Sopranian Understanding node in the Daelic column of the cypher. After you unlock this a quest appears on the map you will need to complete to unlock the Protoform synthesis (mount maker). Once you've done this, the schematics for all of the mounts will now be obtainable.

Serenade requires you to go into the Sepulcher of the First Ones raid and jump don into the pool before the first boss. The trash will start attacking you if you aren't careful. The schematic for Serenade is hidden vertically inside a chain ring in the corner.

Once you've obtained this you will also need to get:

1x Helicid Lattice (kill snails in Zereth Mortis or buy on the auction house).
1x Crystallized Echo of the First Song (on the island where the raid is look for a yellow crystal near the waterfalls).
500x Genesis Motes (Killing most creatures in Zereth Mortis will often drop these)

Once you're done, go back to where you craft the mounts and you will have a new snail friend!

For those like my guild who prefer my video guides, here's a link: https://www.youtube.com/watch?v=PhalbNgsgZs