Divine soul sorcerers are fine. Think about it, there are celestial beings that can be summoned or called to Faerun. While physically manifest, it could be possible they have offspring with a mortal. Their descendants get divine magic not from gods directly, but from their divine beings, some of which are very powerful.
Sure. I could imagine a love story between a cleric and a deva.
Heck, some dragons reside in Seven heavens with Bahamut. Silver dragons are known to polymorph, and can have divine as well as and arcane spells. If they had mortal descendants, they could equally be be divine sorcerers or dragon sorcerers.
This would all be very rare...
Except there are the aasimar, celestial counterparts to tieflings. I suppose if there's plenty of them running around it'd be very uncommon instead of very rare.
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Something worth addressing. Tieflings are not usually found in large numbers, it's just that _all_ the tieflings from Elturel are escaping together that they seem numerous. Also explains why some of them (Rolan) don't feel particularly bound by race.
