A bubble spawner
Spawners are objects introduced in level 14 of Plunger.
Spawners appear square shaped and are dark gold in colour. A circle is seen on each of their four corners. They have an additional hole in the middle of them, one which is square shaped with rounded corners for monster spawners, and circular for bubble spawners.
Spawners remain fixed to a certain area within the level they are in. Periodically, their four circles light up consecutively. After all four circles are lit, a certain hazard emerges from its opening.
The first spawners to appear in the game are bubble spawners in level 14. These entities generate a bubble approximately every seven seconds. The delay in generation is longer when more unpopped bubbles are present on the screen. The lights on the circles brighten in a counter-clockwise formation, starting with the top-right circle.