The three new creatures in this add-on (the gremlin, original cultist, and Nightmare endboss) aren't actually new but rather models from the original game which were eventually dropped from the game. In fact there's an extra map inside Blood II: The Chosen which is basically just a room with the three unused models (they don't do anything, though).
The Blood Wiki (The Blood Wiki, a wiki devoted to the first-person shooter game Blood, its sequel Blood II: The Chosen, and their respective expansion packs. Also available is information on the various mods, fan projects, development details, and the fictional world in which Caleb and the others live in.)
ClydeFrog (10541) added Blood II: The Chosen - The Nightmare Levels (Windows) on Aug 17, 2000