This thing is just for decoration, but it looks spectacular, especially against the night sky. Just make sure that there are no flammable objects around if you build this!
When the lever is pulled, a mini-mechanism makes the main power source's duration last only one tick (0.1 second), and that signal is passed around in a super fast pulser. The visible piston completes the pulser so that the fountain actually turns off when the lever is toggled off.
The pulser's two sides connect with a dispenser each. The dispensers are facing upward with lava source blocks over them. The dispensers are also full of nine stacks of 64 arrows each (576 arrows in each dispenser), so when the pulser flashes on and off, each dispenser fires five times per second.
Although it lasts for just under two minutes, it's preety darn cool. You can even pick up the arrows that have been shot and reuse them!
It looks even better at night!