Unlike in Candy Crush Saga, they are not divided by specific colors. There's one and only look of a mystery egg. They look like partly broken eggs, with a pink question mark on them.
They can be broken by being brought down to the bottom end of the board. That doesn't have to be the very bottom row of a board. For example, a board may not be fully filled with tiles. Bring down the mystery egg to the nonexistent tile and you'll break it. It's interesting that firefly tile behaves like nonexistent tile, in this case. You can bring down a mystery egg to the firefly tile and it'll break.
They can also be broken with a line blast.
It can be affected by blocks' negative effects ("swallowed" by lava, frozen block, etc.)
Mystery eggs, once broken, can result in a few different outcomes:
- + 2 moves
- + 25% Magic Orb meter
- + 2,000 points
- + one specific-color Color Burst on the board
- + one 1-way or 2-way specific-color Line Blast on the board
As all of the so-far known outcomes are positive, mystery egg can be considered an element which makes the game easier.