Ahsa

Ahsa is an enormous serpentine creature living in the methane ocean of Titan.

Red War
During the missions Utopia and Ace in the Hole, Ahsa's shadow can be seen on the windows surrounding the New Pacific Arcology's CPU core in the Festering Halls. The Ghost also mentions that the Arcology's sensors can detect a large object moving underneath The Rig, likely the same creature. Sloane can also be overheard in Siren's Watch talking about something below the waves, claiming that it wasn't her imagination. Guardians have also observed serpentine, finned creatures breaching the surface of Titan's oceans, which are likely Ahsa or other life-forms native to Titan.

During Season of Arrivals, the Drifter makes reference to "the long boy in the soup" when speaking to Eris Morn, likely referring to Ahsa, mistaking the creature's gender.

Trivia

 * Before Titan was moved to the Destiny Content Vault, if one went beyond the normally player-accessible areas of Titan and managed to see below the surface of the ocean, they could see . These are likely intended to be the dorsal fins of the sea serpent breaching the waves, as normally only the uppermost part of the wheels would be visible.
 * These same fins can also be seen in Savathûn's Throne World.

List of appearances

 * Destiny 2
 * Shadowkeep
 * Season of Arrivals
 * Lightfall
 * Season of the Deep