Collisions is an atmospheric puzzle game. The puzzles vary from one screen to the next: some are easy, others require timing, logic and anticipation. Players advance by indirectly moving a black ball. The gameplay mechanic involves using various physics-based contraptions like plungers, flippers, gears and sliders. The game provides hints in proverb form that explain metaphorically how the different contraptions are used.
The game begins with a small, star-like object appearing in the sky that grows and can eventually be recognized as a comet. There is no explicit story in the game, but events involving the comet do occur in the background. The ending can be quite surprising too, especially for players that have not been paying attention.