I have some trivias Valak’s appearance in Conjuring 2, and I can somewhat compare it with “demonology” in my own country. Basic fact, Valak is a part of 72 demons appeared in the Lesser Key of Solomon, a “guide book” for magicians to perform their rituals. He is one of the Hell’s president who commands 30 legions of demon. He is also the summoner of snakes and serpents. As a president of hell, of course he is a very strong demon, that is why he is depicted as a nun in Conjuring 2. In Christian demonology, the stronger the demon, the more it mimics the Christian aspects, that is why Valak takes a form of a nun, complete with the cross on his neck. This is also happened in other movie. In the legendary movie the Exorcist (1973), the strong demon, Pazuzu is also using cross in an inappropriate way without being burned.
Another interesting fact to support this theory is the occult belief of the Witching hour, at 03:00 am. Witching hour is the time for witches and demons to do their stuffs, many bad stuffs happened at those time, it is the inversion of 03:00 the time believed as the time when Jesus died on the cross, a mockery.
In islam, there is also this kind of stories. Many times, I heard story about how a santri being possessed, and while being exorcised in islamic way (by reading prayers, especially the Ayat Kursi), the Djinn inside the santri is following the prayers (and ultimately finished it) then laugh at them in mockery. It is indicated that the Djinn possesed the santri is a strong one as it is strong enough to make them recites parts of Qur’an.
Interesting comparison between Christian and Islamic demon (syaitan) would be how they depicted in daily modern life, either by movies or myth. In Christian side of the story, it is often be told that demons are the rebels of God. They rebel against God, and condemned to hell. Their rebellion against God and their status as a rebel is more commonly depicted.
While in islam, demon/syaitan (and syaitan in form of jinn) are also defecting from God’s order to bow for Adam, which ended up hating Adam’s heir to eternity, swearing to disturb them forever. What they do to mislead human into misery is what often told.
Well, I think that’s what I get from Valak’s character. It’s haunting for sure, but I like it so much.