Asmodeus

The tieflings connected to Nessus command the power of fire and darkness, guided by a keener than normal intellect, as befits those linked to Asmodeus himself.

Ability Score Increase Int+1

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Infernal Legacy

You know the Thaumaturgy cantrip. Once you reach 3rd level, you can cast the Hellish Rebuke spell once as a 2nd-level spell. Once you reach 5th level, you can also cast the Darkness spell once. You must finish a long rest to cast these spells again with this trait. Charisma is your spellcasting ability for these spells.