I should clarify that the final forms do give extra buffs~
Darker form: more damage
Incubus: 50% chance of aphrodisiac effect and slightly more damage,
angelic: 100% chance of pacifying effect.
I should note the pacifying effect is slow to react at the moment, and less obvious when you use it, the holy water bottle has this effect, it takes roughly 30 seconds for it effect. but it can stop insta-kill enemies