When you set this scheme in motion, each opponent sacrifices a creature of their choice. Then each opponent who didn't sacrifice a creature discards two cards.
Only Blood Ends Your Nightmares is not legal in any format.
Rulings
2010-06-15
Each opponent who can sacrifice a creature must do so, and thus won't discard any cards. Each opponent who can't sacrifice a creature (either because they don't control any, or because they control Tajuru Preserver) will wind up discarding two cards. Your opponents have no choice in the matter.