Carefully read the instructions, even for games that you already played. The rules may have changed. For instance, in the "pawns" game you are asked at first to end up with four pawns. Later you are instructed to only have two pawns.
Check behind the portrait of Titus in the main hall to find a safe. Click on the buttons on the safe to spell "MAGIC BOOK" and unlock "The Creature" bonus level.
