How do you get wish cave on mystery blue dungeon?

It seems you're talking about the game Mystery Dungeon: Shiren the Wanderer, not Mystery Blue Dungeon. The Wish Cave is not a location in that game.

However, there is a way to access a Wishing Well in Shiren the Wanderer. This is how you find it:

1. Complete the game once. You need to have finished the game at least once to unlock the Wishing Well.

2. Find the Wishing Well: The Wishing Well is located in the "Wishing Well Room" in "The Cave of Forgotten Dreams"

3. Use the Wishing Well: Once you find it, you can use it to make wishes by using specific items and offering them to the Wishing Well.

Important Note: The Wishing Well doesn't guarantee you will get what you want. It's more like a random chance, so you might get something helpful or completely useless.

Let me know if you have any other questions about Shiren the Wanderer, or other Mystery Dungeon games.