I'm fairly certain that it was about a boy who got something from his grandfather that lead him into this massive underground realm with magic. He meets this group of people about his age that save him from a common danger in this realm. He turns out to either have a weapon or a pet that becomes either a weapon or battle steed and he joins this crew to learn how to use it and defeat these things.
There's also another boy that's such a drama queen about having a dark past and pushing his body to the extreme to become stronger

Did the main character have a striking resemblance to Jaune from RWBY?

I honestly have no idea. This was YEARS ago

Is it Huntik by any chance?

I don't think so

Can you describe the art style?

Like... A kids anime. A less refined version of Pokemon. Something that looks cheap

Is it Magi-Nation?

That looks familiar. I think it was. Thank you!

You're welcome. I didn't think there were animations of such low quality out there. It has been a spiritual journey for me.

Oh you should see Dino Squad, it's horrendous