As Kirby: Squeak Squad’s main gimmick was using bubble items and the Copy Palette, which has not returned since (although Assist Stars are similar in concept to food bubbles), Bubble has not made an appearance in any other game; however, there has been no formal statement that Bubble will not appear again. Bubble was even considered for Kirby Battle Royale as a Copy Ability that could be voted into the game.
Kirby winds up, then fires a single large bubble that flies forward then curves up. While Kirby charges up this bubble, the direction of the bubble can be influenced by pressing up or down. This bubble instantly turns any regular enemy into a bubble.
Mysterious bubbles can capture so much.
Bubble Kirby's got the power to turn enemies into soap bubbles.”
Bubble was originally conceptualized as a Copy Ability the character Sharbon would give if Kirby inhaled him. This ultimately did not occur, however.
In this instance, Bubble Kirby's appearance has Kirby covered in soap bubbles.
The developers had a difficult time deciding what Bubble's ability hat should be, as bubbles are flexible and do not have a defined shape. The team eventually settled on the current design: a shower cap, specifically one used by Japanese children to prevent soap from running into their eyes. This design was met with some resistance, as some team members pointed out that Kirby does not have hair (though other members would make the counterpoint that Kirby's eyes would still need protection against soap foam). Additionally, the developers did not know if the shower caps were still used by children in 2006; the team looked in shop windows to see if the caps were still being sold.
In the E3 footage for the unreleased Kirby GCN, a Copy Ability (most likely Water) was shown. It demonstrated only one attack: Kirby blows bubbles that spread around a fair distance, very similar to the Bubble ability's main attack. The Bubble ability debuted in Kirby: Squeak Squad one year after Kirby GCN’s trailer was shown; Bubble may have drawn inspiration from Water.
Kirby of the Stars Copy Ability "Bubble" Introduction Video