Alrighty guys. Here's a theory I have about the final boss.
I won't put it into spoiler tags, because you know, it is just my theory based on some thoughts and logic conclusions that I made and that I want to discuss with you.
The achievement list doesn't say anything about Alucard. What if at the end of the game Dracula will team up with Alucard to fight Satan. But then something unexpected might happen. Maybe they will do something similiar to Symphony of the Night. Remember, when Shaft controlled Richter? Well something similiar might happen to Alucard. Satan, being someone who likes to possess all kind of people throught history takes control of Alucard and tries fighting Dracula in the body of his beloved son. Would be pretty tragic if you ask me. Now, there's two possible ways of ending the game... the bad ending would occur if Dracula would fight Alucard and kill him and thus also kills Satan. Tragic, yet he saved the world once again. Of course similiar to what occured in SotN you didn't fight the true final Boss, thus the game ends a little bit earlier and you won't unlock the Boss Rush mode since you didn't fight all of the bosses in the game.
And just like Spainkiller, it won't take you around 20 hours to complete the game. Remember, Cox said there would be a possibility to refight bosses and there's also supposed to be optional bosses? Plus this way Satan would be able to revive again pretty soon. Open end.
Now here's my theory for the good and true ending (that similiar to SotN would be the canon ending for the game and the series as a whole):
You can try finding a way to either prevent Satan from possessing Alucard or find a way to drive him out of Alucard without having to kill him. After that the true final Boss fight of the game would occur: against Satan in his black winged angel form and against his true form, the Leviathan.
Now in order to do that you would either have to find everything, complete a certain challenge or find a certain item that allows us to somehow free Alucard from Satan's influence. Said item might be guarded by a secret or optional boss (Dave told us that there would be at least one optional boss on a hidden path). So searching for and finding that optional area, clearing it and fighting the true final boss would enhance the game time to nearly 20 hours (or in the case of Spainkiller maybe to 17 hours).
I mean that leaked level list was pretty accurate. And it did mention the Leviathan at the end so I just doubt that the final battle is „just“ against Alucard. If it is, we cannot change that and need to find joy in the other bosses (like the Toy Maker, the Gorgon, Carmilla, the Acolytes etc.), but honestly I doubt that this will be the case and that MS might have done the same thing SotN did. Sure there won't be a whole new area to explore like a mirrored castle but there might be a true final boss leading to a good ending.
Finally Cox mentioned that one major boss/ character wouldn't be listed on the achievement list. And that one guy just might be Alucard.
What do you think about my theory?