What do you mean by secrets?
According to legend, Mt. Coronet is where the Sinnoh region began. Arceus created Dialga, Palkia, and Giratina at the Spear Pillar, as well as the Adamant, Lustrous, and Griseous Orbs, then fell into an unending sleep on the highest point of the mountain. -Bulbepedia
- You can get Dialga, Palkia, and Giratina.
- Feebas is only found in Mt. Coronet
Read this page for more information
Again, I don't know what you mean by secrets. If you could comment, that would be really helpful.