Let's assume the following situation: On the battlefield on my side lying these permanents: Open the Graves, Thallid Soothsayer and another non-token creature. My opponent is attacking me with two creatures.
Am I supposed to do this: With my non-token creature I block one of the creatures of my opponent. Then I sacrifice my creature with Thallid Soothsayer so I get a token Zombie creature. Can I now block the other creature of the opponent with the token Zombie creature?