There are a lot of reasons why it wouldn't work or would be one or the other, but by the Rule of Cool I'd want it to be a hybrid.
Tiefmar
Appearance: gray feathered wings, short tiefling-like horns and tail
Ability Score Increase: Charisma +2, Wisdom +1
Age: up to 120
Alignment: often chaotic neutral
Size: medium
Speed: 30'
Flight: 30' (for 10 minutes total, regained on short or long rest)
Darkvision: 60'
Abomination Resistance: resistance to necrotic & fire damage
Abominable Touch: As an action, you can touch a creature and cause it to regain 1 hit point; when you do so it creates a bright harmless flame at the point of contact accompanied by a booming sound and smell of sulfur. Once you use this trait, you can't use it again until you finish a long rest.
Languages: common, celestial, and infernal
[MENTION=6875235]Elon Tusk[/MENTION] No, no the feathery wings attached to its nose and the horned tail protruding from his navel surely qualify this as a mongrelman.
[MENTION=6875235]Elon Tusk[/MENTION] No, no the feathery wings attached to its nose and the horned tail protruding from his navel surely qualify this as a mongrelman.
For the adventure I've been writing for the last thousand years or so, a Tiefling hero and his Elven wife have a daughter who is basically a half-elf with just a few infernal traits (enough to make her VERY valuable some really bad people). But having read Elon's suggestion, I think I'll consider creating an elf/tiefling hybrid, that's much more interesting!