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. Because of the sprites' placement in the game's data, it's speculated that this ability was replaced by the UFO ability.

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 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

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.

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

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.

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.

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.

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 introduction to Vegetable Valley's main theme is inexplicably altered in the European release.

According to Masahiro Sakurai in a video uploaded to his YouTube channel, the game started out as a requested NES adaptation of Kirby's Dream Land, but Sakurai and HAL Laboratory successfully negotiated with Nintendo to make a new game in the series for the home console instead, which became this game. Sakurai also said he and his team wanted this game to be on the SNES, but they simply didn't have the money or resources at the time as HAL was also on the verge of bankruptcy.

Because the NES had a higher resolution and the fact that it, in general, could fit more on screen and allow for bigger environments, Masahiro Sakurai claimed to have problems with Kirby's float ability as it became far more powerful then it was on the Game Boy. The game director and his team cleverly resolved this by creating the game's large information panel UI on the lower-third of the game screen, which was also perfect because the developers could show off unique artwork and info to the player based on the game's new copy ability system.

Part of Grape Garden's background music greatly resembles the song "Silver and Gold", sung by Burl Ives, from the animated holiday musical film "Rudolph the Red-Nosed Reindeer".