Eidolon Gantulyst

"Legends say the Gantulyst wields an enormous boulder for an arm and radiates powerful beams of Sentient energy. The Ostrons built a shrine in its honor hoping to gain its favor."

Gantulyst are gigantic spectral Sentient creatures found on the Plains of Eidolon at night. They are remnants of a Sentient that was defeated in a battle against the Tenno during the Old War, whose remains now wander the plains perpetually searching for their lost components. These fragments are, however, still formidable creatures armed with powerful attacks and near-impenetrable defenses, and are hostile to both Tenno and Grineer alike.

Summoning
Tenno should capture Eidolon Teralyst and then offer their Brilliant Eidolon Shards on Eidolon altar in the middle of the lake