What I think will happen in The Crystal Empire Part 2

1: The Ponies realise that the Diamond dogs are trying to sweep the entire land of crystals and are working for the illusive King Sombra.

2: Spike finds out where Rarity has been imprisoned and devises a plan to release her. They then decide to find the other ponies together.

3: When the Diamond dogs learn that Rarity has escaped, they give chase. Led by King Sombra, they track down the Ponies. They capture all 6 of them (and Spike) and take them all to e dungeon. Spike then reminds Twilight that she can use her magic to use one of the crystals that Rarity has found to communicate with Princess Celestia.

4: Princess Celestia asks Princess Luna to look after Canterlot while she goes to rescue the ponies from King Sombra.

5: King Sombra removes all crystals from the dungeon to prevent any further escape attempts by the ponies. However, Princess Celestia arrives just in time to free the ponies and together, they restore peace to the crystal empire by giving back it's treasures. Celestia then returns to Canterlot only to find it in complete chaos thanks to Luna.