This is how The Witch Doctor arrives at the Crystal Empire goes in The Crystalling Part 2.
[Princess Cadance feels a shiver]
Shining Armor: You okay, Cadance?
Princess Cadance: He's back.
[The Witch Doctor appears]
Witch Doctor: Good to see you again, Celestia.
Princess Celestia: We never had a pleasure meeting, Aldous.
Witch Doctor: I've changed since you last saw me on Quatros.
Princess Celestia: The planet where