Baldur's Gate 3 - Tiefling's Infernal Legacy: Unleashing the Flames of Hell
Tieflings have a racial trait called Infernal Legacy. This gives them bonus spells at levels 3 and 5. This video covers the bonuses that are available to Mephistopheles (Burning Hands and Flame Blade), Zariel (Searing Smite and Branding Smite) and Asmodeus (Hellish Rebuke and Darkness) tieflings.
