With a barrage of effervescent soap bubbles, Kirby can turn his enemies into bubbles themselves. The type of bubble that an enemy is turned into is determined by what ability it would give under normal circumstances. As for enemies that don't give abilities, they are turned into bubbles containing stars instead. If swallowed and then tapped on, the star bubble becomes a star to be exhaled. A Gold Waddle Dee will also turn into a bubble containing a star, but additionally, a Treasure Chest will be dropped in the same place.
Kirby creates a stream of bubbles from his wand, which turns regular enemies into bubbles when their health is fully depleted. While holding B, the direction of the bubbles may be changed by holding up or down.
Kirby rears back for a split second, 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 angled upwards by pressing up. This bubble instantly turns any regular enemy into a bubble. This move requires the Ability Scroll.
Mysterious bubbles can capture so much.
Bubble Kirby's got the power to turn enemies into 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