Lux's Deus Gigantia had two forms.
The first form was its regular form, where he would summon a Skeleton King that would always be a Rank Higher than him and would always be a World Boss Monster.
Currently, Lux was a D-Ranker, so when he summoned Deus Gigantia, a Skeleton King with the rank of a Dreadnaught-Ranked World Boss, would appear.
But that was only its basic form.
Deus Gigantia's second form would allow all of Lux's Undead Legion, Named Creatures, as well as members of his Covenant to merge with the Skeleton King, absorbing 20% of all of their Maximum Stat Points. Compared to Leonidas' Unique Skill, Power Assimilation, this was no doubt the better skill.
However, this skill had its drawbacks.
Once Lux had used this skill, he wouldn't be able to summon his Undead Legion and Named Creatures, except for the members of his Covenant, to aid him in battle for an entire day.