Cressida Cowell 
Yr Hudlath a»r Haearn — Y Ddau Ddewin [PDF ebook] 

Enter a land of wizards, warriors, mythical creatures and powerful magic in an exciting fantasy adventure from the author of
How To Train Your Dragon. In the second title in the series, Don possesses a powerful Magic Spelling Book and Llyr has a dangerous Witchstain on his hand. It was unlikely that these heroes should meet in the first place; is it possible that they will meet TWICE?