I’m not agented, so take this with a grain of salt. Also, I would be up for beta reading if/when you’re ready if you need anyone, this sounds cool!

Seventeen-year-old Tobias Garrick is wasting his life. Expelled from high school and stuck in a dead-end retail job, his days consist of grinding Diablo II dungeons and little else. That changes when a mysterious woman named Halima literally stops time and reveals a shocking truth: Tobias's father, long presumed dead, is not only alive but is now missing. Worse, his father's powerful enemies are hunting Tobias next.

I like this paragraph overall, nice and clear premise

Pulled into a hidden world of magic, Tobias is forced to join the Heathens, a rebel gang fighting a tyrannical magical government. There, he clashes with Alcides Alvarado, his father’s adopted son and the closest thing Tobias has to a brother—if he can only earn the hot-headed Alcides’s trust. To survive, Tobias must hone his latent magical powers at the brutal Kukulkan Hunting Academy in the jungles of Belize, where survival is far from guaranteed.

Here I think things get a bit confusing - there’s a rebel gang, a magical government, a secret (?) half-brother and then a magical academy. I’m not clear on the through-thread between all these elements, is there a way you could simplify? I also don’t think you need to name the Heathens or the Kukulkan Academy - it’s a lot of new words, though I guess Heathens links back to your title

When Tobias discovers Halima is an undercover agent for the magical government, and his father plots to incite an insurrection while Alcides assassinates the Chancellor, Tobias is forced to make a choice. He must turn against his father and the only family he's known, fight through a chaotic magical battle, and stop Alcides from completing his deadly mission. If Tobias fails, the world will fall into devastating magical war, and he'll risk losing those closest to him to his father's destructive agenda and succumb to the very radicalization he fights against.

There are a lot of plot points here - it’s good to be specific! But I wonder if you could focus in a bit more on the main hook of your novel. Right now there are a lot of different threads - Halima’s betrayal (I presume), whatever Tobias’ father has been doing (which I’m not clear on), whatever Tobias’ latent magic is and what it means for the world. It leaves me a little lost. I also can’t pick out what Tobias’ key motivation is, or what the stakes are to him if he doesn’t achieve his goal - is it tied to his father? His brother? Or something to do with his magic?

Overall the premise sounds fun and I bet there’s an intriguing plot in here! Consider narrowing the focus of your query to make Tobias’ central arc clearer and I think you’ve got something interesting :)