I see Graham appearing early in the game, and I feel that he should stick to his first form - changing forms would make him seem too final-boss-ish. And rather than swiping moves from Dracula (his similarities to Drac are already what's keeping him out), he could instead use the moves he already has (hellfire, 2 patters of magma balls) plus his lightning generator from his second form.
Well, you see...
Graham is one of the dark lord candidates. By what we saw already, the dark lord candidates possess specific parts of Dracula's power (Dario possessed fire powers and Dmitri, copying abilities). Graham possessed what? Fire power...?? So, he had the same thing as Dario...? Although that's how it worked on Aria (because I
slightly believe Konami is not taking Serio's game canonically xD), I think we
could provide an explanation to that here, on a golden chance.
I think that we could say that, Graham got the fire powers, but his Dracula part was always Dracula's aversion to religion/morphing powers. Allow me to ellaborate: Graham is able to transform. Dracula could do that. Into what does Graham turn? Into a freakin' twisted mockup for an angel (which seems like "corruption of holyness" if you ask me). So, I think Graham's inherited power is the morphing ability. Now, from where did the fire power come from??
EDIT HERE: I'm fully aware that Dario came after Graham, and thus, the original fire owner must've been Graham, but still~Remember what happens when a candidate tries to use power that's not his? He breaks. Either turns mad or dies, or both. Dmitri displayed this very shockingly, and Graham displayed it too... Although on Aria it looks like "becoming crazy" was his nature, I always though it was too abrupt. I mean, in one moment he was that collected, smart man. The next (after a HUGE chunk of no-cutscene playing) he's already a crazy cook. We don't see a *clear* explanation, asides some lines from characters who seem to have met Graham, for why his fall into crazyness. So, why not explore this on this game? Why not say that he *obtained* his fire power on Uber Dimension, while Aria happened? He could have been transported to Uber Dimension while trying to breach through the Dark Gate on Floating Gardens. Why couldn't Soma do it? Because (besides the "you need to realize you're Dracula" thing, which seems kinda farfetched seeing as Dracula's soul is there, you knowing or not)
there is already a Soma from the same timeline on Uber Dimension, thus prompting the Dark Gate to avoid a paradox by not allowing Aria Soma to enter it (This doesn't apply to other characters since this can be a property of the Dark Gate only).
One thing I'd like to point out about Graham. Remember how he displays a level of madness
only after he acquires a red aura and teleporting powers?
So, how did Graham get the fire powers?
IF Graham is playable, this can be explained as "Graham killed Uber Dracula, and, by being a part of Dracula himself, he got *acknowledged* as a candidate for the position of dark lord (again!) and inherited one more power by Dracula's shattered soul, carrying it back to Main Dimension, and strenghtening his belief he's the true Dracula (and progressively destroying his mind), or "Uber Dimension, being the main dimension affected by Uber Dracula's leaking power, allowed Graham do bid part of it on his own, while there, allowing him to produce fire".;
IF Graham is a boss, he could have gotten the fire ability by being fused with a fire demon, by Shaft or another of Dracula's priests/sorcerers. Celia could do it, why can't they do it too? Shaft can summon demons, much like Celia. He's one good bet. By defeating boss Graham, he wouldn't die, but stay "beaten" (like Stella, Richter and Barlowe do in some stories) because "the hero feels like he can go back to normal, he's only a missionary under Dracula's influence" which is a mistake by the hero's part, prompting the events of Aria.
Playable speaking, I picture Graham like a playable Dmitri. He has a knife too, remember?
EDIT: Slight point here. I'd prefer to think that Graham *gained* the ability to transform, instead of fire power. I mean, he can transform because Uber Dracula's shard granted even more power to him. But only if the "Graham has fire powers, so Dario has fire powers too?" can be sorted out on a creative manner...