Vomvalysts are small, hovering Eidolons that roam the Plains of Eidolon that transform into spectral beings after sustaining enough damage, making them immune to all forms of attack, the OperatorVoid Beam being an exception.
The Teralyst is the first-tier bipedal Eidolon boss found roaming at nighttime.
The Gantulyst is the second-tier bipedal Eidolon boss that is significantly larger and more mobile than the Teralyst.
The Hydrolyst is the third-tier bipedal Eidolon boss, capable of channeling thunderstorms.
Eidolon Lure - Grineer machines found at night on the Plains of Eidolon used to capture Eidolons.
Ropalolyst - A flying boss that roams in the sector next to Ganymede, Jupiter. Though not referred to as Eidolon in-game, it was commonly referred by both the community and the developers as the "flying eidolon".
Though not referred to as an Eidolon in-game, both the community and developers often refer to the Ropalolyst as "Flydolon" ever since Devstream 100. However, its location then was moved to Jupiter. The boss fight shares a lot of similarities with the Eidolons fights, such as the Synovia weak points and shields which can be depleted using the Operator's Void Beam.
Interestingly, Eidolons are also possessing spirits in Greek mythology, and they could control mortals and monsters alike. Perhaps the Eidolon Vomvalyst's spectral form could be a reference to the spirit form of Greek Eidolons
Eidolons (and the Ropalolyst) feature weak points called Synovia. In real life, synovial joints are joints in the body filled with synovial fluid, such as the knees, wrists, and elbows.