BTW, do tieflings look like that because of 5E? They all look the same, i thought the demonic traits were supposed to be varied and sometimes hard to spot?
Even in 2E, you had horns, scales, goat legs and rat tails. Not necessarily hard to spot in most cases.
But yeah, 5E seemed to boil it down to "horns".
https://www.dndbeyond.com/races/7-tiefling
Tieflings are derived from human bloodlines, and in the broadest possible sense, they still look human. However, their infernal heritage has left a clear imprint on their appearance. Tieflings have large horns that take any of a variety of shapes: some have curling horns like a ram, others have straight and tall horns like a gazelle’s, and some spiral upward like an antelopes’ horns. They have thick tails, four to five feet long, which lash or coil around their legs when they get upset or nervous. Their canine teeth are sharply pointed, and their eyes are solid colors—black, red, white, silver, or gold—with no visible sclera or pupil. Their skin tones cover the full range of human coloration, but also include various shades of red. Their hair, cascading down from behind their horns, is usually dark, from black or brown to dark red, blue, or purple.
Whereas 2E's Planescape Campaign Setting:
They can be described as humans who've been plane-touched. A shadow of knife-edge in their face, a little too much fire in their eyes, a scent of ash in their presence - all these things and more describe a tiefling. No planar would mistake a tiefling for a human, and most primes make the mistake only once.
And the 2E Monstrous Compendium Appendix for Planescape:
Tieflings are the offspring of the planes, as varied as the places they call home. Superficially human, their appearance always betrays them: some sport small horns, other have pointed ears, scales, a cloven hoof, or just a wicked gleam in their eye that never leaves. What they all have in common is a quick temper and a chip on their shoulder. They’re often confused with alu-fiends, erinyes, incubi, and succubi (which they’ll forgive), but never call a tiefling a bastard or a halfbreed. He’ll take it personal-like. Plane-touched is the word, or “sir” or “lady.”
Ironically, I think the way tieflings were in the Planescape setting was born of censorship. TSR wanted to get away from straight up demonic stuff, so that's why we had Tanar'ri and Baatezu
instead of demons and devils. The plane-touched weren't simply demon half-breeds, they could have been anything, or had any trait. Simply having horns alone wouldn't have been acceptable, as it'd be seen as too satanic.
3rd Edition brought the names back, since Wizards clearly doesn't care about being seen as satanic, especially today.
I find it interesting that censoring satanic stuff led to the setting becoming
more creative. But now that the censorship is gone, it's dumbed down into demonic horns on everything.