Yeah I thought so to. The thing is out our own home brew world. Me him and his brother are the creators. Now his class build seems legit. Fire dwarves are allowed in our world and he is a normal pathfinder mage with arcane armor training and a material that lowers the spell save dc the rest of the way. I did have some problems with his spells though. He has everything from 2 different types of instant pit spells to a magnetic spell that lets him rip armor right of of fighters. According to the spell it has a magnetic pull up to 3000 pounds. Its only a lvl 2 or 3 spell. He ripped the breastplate right off a boss enemy lowering his AC by 6 right at the start of an encounter. Said he only needed enough to break the leater straps holdinh it on

. Then he almost ripped his sword out his hand but failed. Only becuase I rolled high and the guy had a strength of 32.... I said I hadnt heard most of his spells and he said that we never restricted what books spells came from. That casters can pull spells from any book. When I argued that fighters should then be able to pull feats from any book everyone said it wasnt the same thing a jumped down my throat... Hes making it a pain in the rear to even make a decent fight. He just rips the clothes off em and drop em in a hole. If they have wings he even has a spell that makes it so they cant fly

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First off, total bollocks. This kid is a powergamer at best, munchkin at worst. Personally, I would call shenanigans and make him make a new character. You're running a low-magic campaign and he's not low magic.
Okay, so a 2nd or 3rd level spell can pull 3,000 pounds? That seems a bit much. What spell is this, anyway? Where is he getting these spells? I've looked through the CRB, APG, UM, and UC and can't find anything that does that.
If you want to make it a challenge, then use things like
ring of protection,
amulet of natural armor, the
mage armor spell...stuff that he wouldn't be able to pull away (which I think is bollocks anyway). Have someone wearing plate mail. That way he can't pull just the front off, it would be the entire suit, person and all, coming toward him.
And not every weapon has to be made of metal. Wooden arrows. Wooden crossbow bolts. Clubs/greatclubs. Sling bullets. Use intelligent encounter design. Use wooden caltrops to make them either use resources to heal or to slow their speed. He can only cast so many spells per day. Make him and the party work for it. No 15-minute work days. If they rest, they're attacked. Use the rules of fatigue and exhaustion.
Have enemies switch tactics. He rips their armor off? Okay, they switched to ranged attacks because their melee advantage is gone. Use waves of enemies and give them Sneak Attacks. Do fire dwarves take extra damage from cold? Use that.
If he's the only high-magic caster in a low-magic setting, he'll have a reputation based on fear and distrust. Maybe people think he's a demon in human form. That could mean no healing at the temple, no rooms available at the inn (leading to more fatigue), traders/craftsmen don't want to work with/for him. Maybe some young gun spellslinger wants to take him down and has 'learned from a Master from over the mountains,' i.e. pulled out some 3rd party stuff of your own. Hell, use whatever you want because it 'wasn't specified.'
Maybe the Fire Dwarves themselves are coming to 'have a talk' with him because of his awesomely fear-inducing powers, common folk are starting to think that
all Fire Dwarves are walking spellbooks and are refusing to have anything to do with the Fire Dwarves.
This guy sounds optimized for combat, so put him in non-combat situations and see how he deals.
Again, total bollocks.