Within the game's data are unused graphics for a an ability that would see Kirby shrink down to a small size. Because of their placement in the game's data, it's speculated that this ability was replaced by the UFO power.

The song in the game's introduction (in which Kirby is being drawn) is based on a Japanese commercial for Kirby's Dream Land, where a child sings the same song while drawing him.

The game contains graphics for an unused 7th stage door. This suggests there may have originally been plans to have 7 stages in at least one hub, but the largest level hub in the final game only contains 6 stages.

According to the Kirby's Dream Collection celebration booklet, a few ideas were cut from the game. Such as Kirby digging holes, turning invisible, multiplying, and even turning into a puddle of water.

Originally there was a cannon icon that would appear whenever Kirby was on a cannon. Even though this was cut from it's original purpose, the cannon icon can still be found by using the Mix ability: it can be seen during the roulette selection of abilities using an emulator's frame-by-frame advance feature. Oddly enough, it remains used in the French version.

At 6 megabits on the game cartridge, Kirby's Adventure is the largest Licensed NES game.

The original Japanese commercial for Kirby's Adventure depicted the game's characters made of yarn. This is thought to have inspired the art style of Kirby's Epic Yarn.

The first letters of the world names (excluding the Fountain of Dreams) spell out VIBGYOR, which is ROYGBIV backwards, a mnemonic used for remembering the colors of the rainbow.

• Vegetable Valley
• Ice Cream Island
• Butter Building
• Grape Garden
• Yogurt Yard
• Orange Ocean
• Rainbow Resort

In Vegetable Valley's second level, there is an easter egg room that can be accessed by moving away from the Warp Star until it disappears. The blocks are stacked to form 'HAL', referencing the game developer's name.

The graphics of an unused ability are stored in the game in which Kirby appears to be mini, similar to an ability featured in a much later title, Kirby & the Amazing Mirror.