The last shot of the impaled Incognito in the last episode is another reference to Vlad "the Impaler" Tepes as this is the same position that he used.
When the dying Incognito asks who Alucard is, there is a lightning strike, which lights up half of Alucard's face to show another face. This second face is obviously based of the portrait of Vlad "the Impaler" Tepes, who is said to be an influence in the creation of the character of Dracula.