Hi, isanatera! Right now this logline is too vague. Right now, it’s the seed of what will hopefully become a really good story. It tells us that the story has secrets, but doesn’t explain what makes those secrets interesting or unique. For example:

You mention a mysterious disappearance of their community, but what exactly is their community? A village? A city? A group of forest animals (you said it’s a fantasy, so if the world is like Narnia, it could be plausible.)

Where is the community located? Urban city? Rural farmland? Way up high on remote mountains?

Animal companion? Is the companion a dog, cat, hamster, horse, Minotaur, etc.? Do they talk or no? What do they add to the story? Are they part of the reason why they are hunted?

What’s their forbidden power? Are they living in a village where he uses forbidden voodoo black magick, where their village normally bands such a practice? Are they psychic? Are they a superhero? Do they fly? Have super speed, etc.?

Prove deadly how? In what way? Executed by a regime? Being hunted by monsters? By losing their companion? By triggering a larger catastrophe?

There’s also no defining trait for the protagonist beyond the fact that he’s young. What’s his flaw? What’s his goal? What does he want? Why is this character the only one who can pursue the truth?

Here’s an example that hopefully helps get your creative juices flowing:

When an imperial purge erases his mountain clan, a teenage shapeshifter and his bonded wolf infiltrate the capital to expose the decree behind it, knowing discovery means public execution.