The Jellyfish, if combined with another Jellyfish, the move is invalid. You can prove it in a level with a lot of Jellyfish. My idea is to add this combo, specially because there is a Coconut Wheel + Coconut Wheel one.
It may consist in:
1) A big rainbow jellyfish will appear and swim off from the sceen, giving you 2,500 points.
2) There will spawn 3 rainbow jelly fishes that will eat candy (like any normal fish) but will convert the candy into normal jellyfish and, in levels with jelly, remove also a layer of jelly.
3) These new 3 jelly fishes will swim off from the sceen, acting like normal jellyfish (spawning 3 normal jellyfishes each from the sides of the screen and eating candy).
This combo will be extremely useful in jelly levels, because the jellyfish can even replace blockers, i.e. Frosting, Toffee Swirls, Licorice Swirls, Candy Bombs, Normal and Dark Chocolate, Sugar Coats, Crystal Candy, Rainbow Twists and Bubblegum Pops; the only blockers where the Rainbow Jellyfish will be able to land in.
The Rainbow Jellyfish won't be able to land in Stripped Candies, Wrapped Candies, Color Bombs, other Jellyfishes, Coconut Wheels, UFOs, Candy Frogs or Ingredients aka Gummi Dragons. If it lands in a Sugar Key, the Sugar Chests will lose 1 layer. If it lands in blockers that are part of the order in Candy Order or in Candy Order Mixed Levels, they will count as part of the order (like if they were shot by an UFO).