Pryzm: Chapter One - The Dark Unicorn is set in a peaceful land where all five races (gnomes, elves, trolls, nymphs and unicorns) have their own kingdom. Unfortunately an epidemic infests all kingdoms except the one inhabited by the unicorns. Of course this leads to accusations and the unicorn Pryzm is sent out to end the plague - she is accompanied by the troll magician Karrock who distrusts her. The player takes control over both of them at the same time: the left analogue stick controls the unicorn and the right one the troll.

The basic gameplay is simple: the player rides through the 16 levels and battles infected flora and fauna. After defeat they transform back to their real selves - if the whole level (including the periodic mini bosses) is rescued the player can proceed to the next one. The roles of the heroes are evenly divided: Pryzm is used for moving at different speeds, jumping and defensive spells, e.g. stun. Karrock on the other hand uses offensive spells and his magic wand to hit the enemies nearby. The game can be played in first or third person perspective.