You have to prevent the poor ball from escaping the dungeon. 3 sides of the dungeon are blocked by walls and the bottom side is empty, but you can summon a wall on bottom side by clicking or touching. Just note that this wall lasts momentarily and you need perfect timing. The ball moves in the dungeon and when it comes to the bottom, you have to summon the wall and block it so it stays within the room.
Touch on mobile device or mouse on PC.