When Gondwana, a supercontinent, settled in the South Pole, glaciers arose that caused a sharp drop in sea levels. This is believed to be the cause of the extinction event that ended the Ordovician Period. The player fight ostracoderms (Jawless Fish) during a sped-up version of this event.
Players deal damage to the boss by attacking the frightened ostracoderms that are criss-crossing the screen. They only appear in the water, which lowers in direct correlation to the boss’s health (boss’s health as a percentage + 10 = percentage of the screen that is water, maximum of 100%). The water has 0.5 times gravity at its top, and 1.5 times gravity at its bottom. These areas move with the water level, going offscreen rather than shrinking. The front of the fish repels, whilst their undersides bounce. Thir topsides act as surfaces. The fish primarily move horizontally at various heights, with little vertical deviation.
Left, right and bottom of the screen and a small area just above the top of the screen. . Whilst the left, right and bottom sides of the play area stop all momentum, the top side flips Y momentum.
The fish are of the classification ostracoderms, from the Ordovician Period. There are gentle waves upon the sea. Glaciers rise in the background, their height opposite to the water. It is a cloudless day in the background.