Regis Lucis Caelum (boss)

Regis Lucis Caelum is a boss in Final Fantasy XV: Episode Ardyn fought at the Citadel at the end of the third chapter. He wields the power of kings opposed by the player as Ardyn Izunia, wielding powers over darkness. The player can roam about the city of Insomnia as Ardyn before the battle to their heart's content to build Ardyn up with his "Descension" ability tree.

Battle
Regis uses various techniques allotted to his bloodline. He can warp-strike, slash with of holy energy, blast lightning and empower his sword with it and strike it down to the ground to unleash frying electricity in the arena. He jumps to have more range, uses Armiger when he has 60%+ health with various techniques, such as sending his arms all attack in a single direction, or scattering them all around, having the weapons surround the player before commanding them to attack. He also wields a defensive formation that if not broken, results in Regis scattering the weapons and having them impale Ardyn. He casts a magical barrier when on the last of his health and can attack while it's guarding him.

Strategy
Though flashy, the battle is not hard, and it is not necessary to max out Ardyn's abilities before facing Regis to easily win.

Trivia

 * Regis's Armiger appears based on its appearance from Kingsglaive: Final Fantasy XV; he wields a unique array of weapons rather than the royal arms, and his weapons are not transparent or glow blue. Ardyn also mimics Regis's Armiger with his signature red glow to the weapons.
 * Regis also uses lightning magic prominently in both the movie and his battle with Ardyn in Episode Ardyn.