The Darmanitan standing around the Relic Castle entrance are waiting for a player to use a RageCandyBar on them. While they are available elsewhere in the world, these versions have a special trait in that once they have below 50% health, they will access Zen Mode and turn into a Fire/Psychic type creature.
In the Dreamyard basement you’ll be able to find a Musharna on any Friday that is equipped with a Telepathy ability that wild Musharnas do not have access to.
If you transfer a Shiny Raikou, Shiny Entei, or Shiny Suicune obtained from a Generation 4 event and visit Lostlorn Forest, east of Nimbasa City, Zoroark, a master of illusion, will appear in the guise of a Legendary dog.
Near the sage in the basement of Relic Castle, toward the end of the maze, you’ll find a Level 70 Volcarona waiting for your challenge.