The Underground Laboratory in Onimusha: Way of the Sword features a mask puzzle that serves as an early environmental challenge for players. Solving this puzzle is mandatory to progress through the laboratory area. The solution relies on observing details within the puzzle room itself.
Upon entering the mask puzzle chamber, four masks will descend from the ceiling. Shizuka notes their resemblance to archery targets, indicating they are meant to be shot with the Oni bow. The correct sequence for shooting these masks is determined by the shadows they cast on the wall and ground of the doorway behind the player.
To discern the correct order, face the doorway leading into the room and examine the shadows cast by each mask. The number of visible openings—eyes and mouths—on each mask corresponds to its position in the shooting sequence. The mask with the fewest openings should be shot first, followed by the mask with the next fewest, and so on.
For those who prefer a direct solution, the masks should be shot in the following order, from left to right relative to the player's perspective as they face the doorway: the second mask from the right, the far right mask, the far left mask, and finally the second mask from the left. An illustration depicts this sequence.
Successfully solving the mask puzzle grants the player the mask key, which is then used in the room containing the Spirit Mirror. The path back to the Spirit Mirror is generally clear of enemies, as any previously encountered foes have been defeated. It is advisable to save progress at the Spirit Mirror and ensure all battle items are replenished before proceeding further into the laboratory, as subsequent areas may present new challenges and enemies.
