The Eidolon Teralyst is a gigantic spectral Sentient Eidolon creature that can be found aimlessly roaming around the Plains of Eidolon at night, acting as one of the Grand Bosses of the landscape. This is the first of the 3-night bosses of Plains of Eidolon, followed by Eidolon Gantulyst and then Eidolon Hydrolyst.

Where do I kill eidolons?

Assuming you survive long enough to drain its shields, an Eidolon Teralyst will become vulnerable to mundane weaponry—but only on the glowing blue weak points at its leg and arm joints. If your team is communicating, it's best to focus fire on one weak point at a time.

What are eidolons in Warframe?

Eidolons are simple-minded, spectral fragments of the shattered Sentient that roam the Plains of Eidolon at night.