None of the other games do Ability mixing the way this game does. Except that some of the abilities resulted from ability mixing returned as "new" abilities in later games: Cutter+Bomb=Ninja (due to Kirby throwing shurikens while using this ability); Burning+Ice=Water (if you try to mix fire and ice, you obtain water; Kirby perfected this combo by the time Magolor arrived in Dream Land); Stone+Needle=Drill (Kirby uses a drill with this combo). The "ability mix" thing from this game is pretty much Kirby's way to learn new abilities.
Shiver Star appears to be Earth (note the continents and moon), but it's completely covered in ice. And there are (man-made) robots who live in a (man-made) factory, but humans are nowhere to be seen.
The state of matters at Ripple Star really drives home the need to stop Dark Matter. It's seen in the cinematic to be slowly being corroded, and indeed each stage looks worse and worse for wear. The horror comes in realizing that this is what Dark Matter plans to do with the rest of the universe.
