wonder mail
No. Because it is hidden. The Pokemon do not know such a place.
24 floors
there are 15 floors in the hidden land.
in the hidden land but you are not able to recruit him there
No, Pokemon cannot be traded in or out of a Mystery Dungeon series game to any other game. However, Pokemon that evolve by trading can still evolve in Mystery Dungeon by using an item known as the link cable, which is found in the game. I know that this item can be found in Solar Cave in the older Mystery Dungeon games, in place of the Hidden Machines found in the locked chambers.
Go to the Hidden Land
there the "x-ray specs" and they reveal hidden stairs and items
In Pokémon Mystery Dungeon: Explorers of Sky, the Ancientpower TM can be found in the Hidden Land. Specifically, you can obtain it by defeating the boss Pokémon in the dungeon known as the "Ancient Relic." After defeating the boss, you'll receive the TM as a reward. Make sure to explore thoroughly, as some items can be hidden in different areas of the dungeon.
Use Rock Smash
In Pokémon Mystery Dungeon: Explorers of Sky, the Silver Veil can be found in the Hidden Land. Specifically, it is located in the dungeon called "The Hidden Land," which is accessible after completing certain storyline events. You will need to navigate through various floors and defeat enemies, and the Silver Veil is typically located on one of the floors within this dungeon.
15f and 8f in the deepest part.
It doesn't have a limit. Even after you go into the Post - Ending, you will still be able to enter it.