If you've ever wondered why it's difficult to remember the events of a dream, it's because a dream's energy is collected in the Moon Kingdom and returned to the world for shape and consistency. Klonoa once had a dream that defied the above reason; he had dreamt about a violent airship crash with a mysterious shadow lingering above it. One day, his dream came true and the ship crashed on Bell Hill. Intrigued, Klonoa and his lifelong friend Huepow set out on an investigative adventure.

Klonoa -- Door to Phantomile is a self-proclaimed guided 3D platformer that entails an epic quest of mystery, item collection, and action. Guided 3D means that although the visuals and levels have been rendered in 3D, players are kept on a predetermined path rather than turned loose in a free-roaming, aimless world. While this is the case, there are multiple paths and various shortcuts in each of the twelve levels.

The world of Phantomile is filled with a wide variety of obstacles, puzzles, and helpful items. Klonoa will encounter a series of locked doors in need of a key, switches that alter the playing field, jumping platforms that provide an extra boost, and automatic and manually powered gondolas. Additionally, the hero will find use in large and small Dream Stones that reward the player with an extra life upon collection of 100, keys to unlock those locked doors, hearts that replenish Klonoa's health, and extra lives.

There are a few specialty items including Phantomilian spheres, Memory Clocks, Ngapoko's Egg, and the Mirror Spirit sphere. Phantomile residents and critters are contained in the dark spheres; by unleashing them, the music plays back a certain way on the World Map screen. If the player goofs up and sends Klonoa to his death, the Memory Clock acts as a checkpoint where the character will respawn. Ngapoko's Egg rewards the player with bonus goodies and the Mirror Spirit sphere doubles the worth of regular Dream Stones.

Klonoa will use his special attack powers to overcome the maniacal critters that roam Phantomile. In addition to utilizing Wind Bullets, he's able to flap his ears and float in the air, execute double jumps, and grab enemies and throw 'em around. His enemies come in all shapes and forms ranging from boss creatures like Ghadius and the evil court jester Joka to seemingly cute Moos and Spikers.