How do you unlock mt mistral in sky?

You can't unlock Mt. Mistral in Sky: Children of the Light. It's already accessible from the beginning of the game. Here's what you need to do:

1. Reach the Isle of Dawn: Start the game and follow the story line until you reach the Isle of Dawn.

2. Find the Entrance: On the Isle of Dawn, there's a large structure with a swirling portal on top. This is the entrance to Mt. Mistral.

3. Go Through the Portal: Fly up to the portal and interact with it. This will teleport you to Mt. Mistral.

Once you're in Mt. Mistral, you can explore the area, collect light, complete challenges, and find hidden secrets.

Keep in mind that Mt. Mistral is a difficult area, especially for new players. You may need to improve your flying skills and learn some basic combat techniques to survive the challenges.