Plot hole: When Vlad enters Mehmed's tent, the entire floor is covered in silver coins and Mehmed remarks on Vlad's weakness to it. There's no way that Mehmed could have known about Vlad being a vampire or about his weakness to silver, as Vlad had killed every Turk after becoming a vampire, so nobody would be alive to tell him. Even the Turk found on the battlefield in the morning lived long enough only to deliver Vlad's message, but died immediately after that.
Character mistake: When Lucian tells Vlad that the creature he encountered is a vampire, Lucian says that "Pi" is Greek for "to drink". "Pi" is actually the Albanian word for drink, not Greek.
Other mistake: When Vlad is in the armory of the monastery, he is standing directly under sunlight. This should have caused his skin to burn immediately and give away that he's a vampire. (00:52:05)
Factual error: When Vlad goes into the Master Vampire's lair a second time, a Golden Knee Tarantula can be seen. These types of spiders are native to the Chaco region of Argentina, South America. Not in Eastern Europe.
Continuity mistake: Towards the end after Dracula bites Mehmed on his left side of the neck, when he lies on the floor there is not blood on it.
Other mistake: Arabic inscriptions can be seen on the golden desk, but the letters aren't connected like normal abjad. This is likely a computer rendering error since some editing software don't natively support foreign characters. (00:17:10)
Chosen answer: Actually, what the master vampire told Vlad is that he will return to mortal after three days if there is no feeding. If Vlad does feed, he will become a new vessel for the dark power, a new offering to the dark. Nothing was said that Vlad would be trapped in the cave but rather a scourge on the Earth. It is true that if Vlad feeds, the master vampire would be set free. After that, the master vampire can take revenge on the one who turned him. A new game of revenge would then be played between him and Vlad.
That's kind of weird because I remember the Master Vampire saying the same thing about Vlad staying in the cave forever too.