Ditto

Ditto does NOT make a appearnce in Ben 10 Alien force however his holagram was seen in Veggeance of Vilgax Part 1. So Ditto was unlocked in Veggance of Villgax Part 1.

GhostFreak

GohstFreak was absorbed in "Ghost Town" by Z'Skyar. But then Z'Skyar took over Ben's body.
So GhostFreak was unlocked in this episode.