Kill both Lunaris and Solaris in the same encounter.
Lunaris, Eternal Moon is the final boss of Act 8. It is one of the bosses of the Solaris and Lunaris fight. The other boss is Solaris, Eternal Sun.
When both bosses are defeated, they are unlocked as major gods in the pantheon system.
Lunaris would occasionally throw her claws. In the Solaris and Lunaris dual bosses fight, she would return to its Celestial Form to aid Solaris, Eternal Sun (and vice versa in certain stage of the fight). In Celestial Form in the Solaris and Lunaris fight, she uses Dark Vortex, as well as fires a “rain of arrow” like skill.
In fact, in the boss fight prior, the orb that suspended in the centre of the boss room of Dusk, Harbinger of Lunaris, was in fact Lunaris in her Celestial Form too. In this variant she has fewer skill set, which only shoot vortex that inflict Dark Vortex.
Solaris, Eternal Sun is the final boss of Act 8.
The boss is one of the bosses in the Solaris and Lunaris fight. The two bosses would not present as humanoid form at the same time to fight the player character. Only one boss would be in humanoid form and then aided by another in orb form.