To answer this question super-late, that's Reinforce — the guiding intelligence of the Book of Darkness — and Nachtwaal, the personification of the corruption of the Book of Darkness. The A's movie, which this seems to be set after, changed the plot around a bit from the series, making the Book's corruption more of a character and less of a boss monster. The snake is there 'cos Nachtwaal has snakes.
