A cartoon series about a young blacksmith in training that got magic powers.
He lives with two girls, a monster and an old man and helps defend the land from evil while learning about his powers.
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That would be Lanfeust Quest (2013), a cartoon adaptation the eponymous French bande dessinée set in the Lanfeust de Troy universe.
In this world, almost everyone has an unique power, and the main character's is being able to melt metal. He happens to be a blacksmith apprentice.
Among his friends are Cixi and C'ian, daughters of Nicolède, the village's typical old, "wise" man. And the monster you were referring to would be Hébus, a troll.
Below is a still of the show's main characters.