According to director Shinya Kumazaki, other characters from throughout the Kirby series were considered to appear in the game as Dream Friends, specifically mentioning Prince Fluff from Kirby's Epic Yarn, Drawcia from Kirby: Canvas Curse, Elline from Kirby and the Rainbow Curse, Shadow Kirby from Kirby & the Amazing Mirror, and Galacta Knight from Kirby Super Star Ultra. These ideas were ultimately scrapped after the developers decided to stick with a set of rules regarding potential additions, such as only allowing one character per game and only using characters from mainline games.

The Version 2.0.0 update adds Marx to the game's cast of Dream Friends; accompanying this is a new fight against him during the credits for Heroes in Another Dimension. While this fight has no bearing on the player's progress, he is actually coded as a full-fledged boss, complete with a health bar and battle music. In normal gameplay, the song, "Vs. Marx — Star Allies Dream Ver.", is only heard when fighting Morpho Knight as Marx. These features can only be seen in action by hacking the game; since Marx has no "ending" programmed for his fight (as it normally occurs during the credits), beating him under these conditions softlocks the game.

Within the game's data are unused models for blue, green, and yellow versions of Hyness. These and his normal model are stored alongside the files for the game's playable cast, implying that he was planned at one point to be added as a Dream Friend as part of the game's DLC, similarly to the Three Mage-Sisters.

The face that Kirby makes when setting the Ultimate Choice difficulty to Soul Melter is an homage to the one that he had in an episode of "Kirby: Right Back at Ya!" when he was possessed by a Demon Frog that made him evil.

In modern iterations of Fighter Kirby's moveset, the charged attack Instant Mega Blast uses the same key combination as Ryu's Hadouken from Street Fighter, likely meant as a tribute to the series.