In Coryoon, you assume the role of a young dragon-presumably with a titular name-as you fly through eight different stages in order to rescue a princess who has been transformed into a little girl and kidnapped by a mysterious evil. Each stage's theme is generally represented by its mini-boss and boss at the middle and end of the level, respectively. The worlds are as colorful as picture books, and the difficulty level itself is relatively low (e.g., Coryoon himself has a forgiving hitbox, the player gets numerous extra lives (up to 9) simply for beating a boss, etc.).
When the game begins, the player has 5 lives and a "vulcan"-like dragon breath weapon that can fire up to three shots on screen at once. If the player refrains from pressing the firing button for around five seconds, Coryoon will charge up his dragon breath and can fire a large piercing shot. The player can change Coryoon's dragon breath depending on which power-ups are picked up, up to three tiers of increasing effectiveness. There are also support-type power-ups, similar to Options or the "!" in Gradius, or the Bits in R-Type.
Power-ups come in the form of orbs dropped by storks, card suit symbols (i.e., hearts, diamonds, etc.) dropped by small enemies, and miniature dragons dropped by large enemies. In all cases except for one (a battle against a sea urchin mini-boss), the storks' orbs will change colors periodically between red, blue, and yellow. If the player picks up an orb a different color of Coryoon's current ability, his current breath weapon will be lost, will change accordingly per the orb's color, and its power will be reduced to the color's base tier.
- Fire: Red orbs will change Coryoon's breath weapon into a piercing flamethrower-type weapon; its shortcomings are that it only fires in one direction and that it does not reach from one side of the screen to the other. If the player collects more red orbs, the length and spread of the fire will increase.
- Ice: Blue orbs change Coryoon's breath weapon into a rapidfire vulcan with a wide spread; its weaknesses are that these shots are not piercing, and that they only fire in one direction. Collecting more orbs increases the contimerous height of each shot.
- Thunder:Yellow orbs change Coryoon's breath weapon into a spread gun-like thunder weapon; while it eventually fires in seven directions simultaneously, the thunderbolts have small hitboxes and its rate of fire is slightly less than that of Ice. Collecting more orbs increases the number of directions the thunderbolts fire in.
- Heart: Gives Coryoon two fairies that rotate around him and will both hit enemies at close range as well as absorb enemies' bullets. If the player holds down the secondary button, the fairies will lock in place at the top and bottom of Coryoon.
- Spade: A bomb. If the player presses the secondary button, all enemies on the screen will be destroyed. It doesn't work on boss enemies.
- Diamond: Shrinks Coryoon's hitbox, similar to the "Minimize" shield option found in the Gradius series.
- Miniature Dragon: A small dragon helper appears and flies randomly around the screen attacking enemies. Its effect depends on its color: blue dragons will fly around damaging any enemies they touch; red dragons will fire single vulcan shots; and yellow dragons will shoot the first-level three-way thunder breath weapon. They will leave once the player reaches the boss of the stage.