Hello, thank you very much for playing the game and reporting the bug!
Warning, spoilers ahead:
I suggest starting with the easiest route: first the Kraken, then Shaytan and finally the Lindwyrm.
Head to the beach and walk through the shallow waters, but stay close to the shoreline. When the creature emerges from the sea, run as fast as you can toward land and confront it there. Fighting the Kraken on solid ground removes the terrain advantage it has in the ocean, making it significantly weaker and much easier to defeat.
After defeating it, use the book you obtain to teach Ariela a new technique called "Great Typhoon Blade". This skill deals extremely heavy damage to Shaytan, as he is highly vulnerable to water-based attacks. However, the most important advice I can give is: try to blind him. Most of Shaytan's attacks will fail to hit you while he is blinded.
Finally, learn the new ability granted by the book and try to reach Level 8 in order to unlock Ariela's "Annihilation" technique. This skill can inflict the Stun status effect on the Lindwyrm. However, once you have learned "Inner Power," it is still possible (though quite challenging) to defeat the Lindwyrm before reaching Level 8 with Ariela.
Doing so is highly rewarding, because upon defeating it, you will obtain a book that teaches "Meteorite Blade", an rock-element technique that will be extremely useful when exploring the North Forest.
