If Kirby manages to copy two Special Powers at the same time, he gains a powerful ability called a Power Combo. Combine different Special Powers for entirely different Power Combos, or combine two of the same Special Powers for a super-powered version of that ability!”
Once you have one special power, you'll be able to mix it with another power-up to boost your abilities. Hit L, R or any C Button to spit up your current power, which will appear as a star. Hurl it at another enemy with special powers, then swallow the new, more powerful star that appears.”
In Kirby: Squeak Squad, obtaining the Ability Scroll for Sword or Bomb allows either to be mixed with Ice or Spark (as well as Fire in Sword's case) to create elementally-enhanced versions of the ability. This is usually accomplished by mixing ability bubbles.
In Kirby Star Allies, various Friend Abilities also allow a Copy Ability to be elementally enhanced, this time also including water and wind elements. Certain Friend Abilities also resemble Power Combos, most notably Stone's Curling Friend Abilities.
Kirby of the Stars Special Ability "Power Combos" Introduction Video