Wario Land 3: Part 91: Castle of Illusions (Blue Chest)

At 1:05, the Castle Brick from the West Crater's Green Chest is installed into gaps in the level. You then move through a doorway into a new room where you break through Enemy Blocks. After leaving, head to the room at 2:23 to find the second gap filled with a Castle Brick. In the next room, use an Owl to fly through the newly created Enemy Block opening, navigate spikes, and reach the Blue Key. Exit through the rightward doorway and the Blue Chest appears in the following room. The Blue Chest contains Rust Spray, which weakens grey iron walls in The West Crater, The Steep Canyon, and the Cave of Flames, making them easier for Wario to smash.