The worlds could merge through a magical portal. For instance, a wizard in the Harry Potter world accidentally creates a portal to the land of Jack the Giant Slayer while experimenting with a new spell. Then, characters from both sides start to interact. The wizards could teach the people in Jack's world about magic, and Jack could teach them about his skills in fighting giants.
One interesting concept could be a magical crossover where the giants in Jack the Giant Slayer are influenced by the magic from Harry Potter. For example, perhaps some giants have wands and can perform basic spells. Another idea is that Hogwarts students go on an adventure to the world of Jack the Giant Slayer as part of a special magical studies project. They could use their knowledge of magic to outwit the giants.
It was not Jack the Giant Catcher, it was a modern novel that had nothing to do with fairy tales. It was originally written by Faulkner in England and published in 1958. It was a modernist novel full of fantasy and black humor. Although its name contained the words " Giant Catcher," it was not adapted from any fairy tale.
The ending of the Demon Slayer manga sees the main characters achieving their goals and finding some form of peace. But to avoid spoilers, I suggest you read it yourself to experience the full impact.
The ending of the Demon Slayer manga is a mix of closure and hope. The heroes overcome the challenges, and there's a sense of a new normal emerging. It ties up loose ends while leaving room for imagination about the future of the characters.
The Never Ending Story 2 has a different cast from what would include Jack Black. Jack Black is typically associated with his own brand of comedic acting in other projects, not this sequel. His acting style and the overall tone of his work don't really match what The Never Ending Story 2 was aiming for in terms of casting.
I'm not entirely sure specifically what 'rock giant never ending story' refers to without more context. It could potentially be a story about a giant made of rock that has an unending or very long and complex plot.