How to Play
Balloons ▲ float up. A balloon is valid only if the cell directly above it is the grid top, a black wall, or another balloon.
Iron balls ▼ sink down. An iron ball is valid only if the cell directly below it is the grid bottom, a black wall, or another iron ball.
Goal: Every region (bold-bordered area) must contain exactly one balloon and one iron ball.
Tap a cell to cycle: empty → balloon → iron ball → empty.