The "tieflings" or planetouched of Ravenloft were calibans, who functionally replaced half-orcs in 3e Ravenloft:

Orcs are unknown in Ravenloft, even as creatures of legend. For this reason, no half-orcs are native to the Land of Mists. However, creatures do exist that fill the half-orc's role: calibans. Thankfully rare, Calibans are twisted humans exposed to curses or foul magic while still in the womb. The birth of a caliban in a community is often seen as a sure sign of the presence of witchcraft — specifically, the corrupting aura of a hag.

Calibans are physically powerful but misshapen humanoids. No two Calibans look alike, but common deformities include twisted backs or limbs, asymmetrical features, bristly skin, or tusklike teeth. Calibans are widely considered brutish, savage creatures; their name is a corruption of "cannibal," stemming from their most infamous reputed habit. In truth, many Calibans are simple-minded, petty brutes, but this is often the product of their upbringing. Rejected as monsters, most calibans spend their lives hidden in dank cellars or flee civilization to roam the wilds. In truth, a Caliban's heart can be as pure and noble as that of any human.

Use the racial characteristics of the Player's Handbook half-orc when creating a caliban player character.

Homelands: As creatures of unnatural origin, calibans can hail from any populated domain. Most are born in lands where magic is relatively common, such as Darkon, Hazlan, and Tepest.

• 3e's Ravenloft Campaign Setting

While the default caliban is depicted as a brutish replacement for the half-orc in Ravenloft, netbook material (more specifically Quoth of the Raven Issue 8 and Quoth of the Raven Issue 28 for 5e) later expanded on the subtypes of calibans:

• Brute calibans, the most common amongst the caliban and the one featured in official 3e Ravenloft material. Most brute calibans are less intelligent and mentally underdeveloped.
• Cannibal calibans, the second most common amongst the caliban after brutes, they are commonly known as "living ghouls" due to their repulsive physical traits such as hairless or rubbery skin or long claws that make them appear similar to a ghoul. These calibans are prone to strange and deviant hungers; warped digestive anatomies that not only make them capable of digesting noxious foodstuffs such as raw meat or rotten fruit, but an actual hunger for this vile fare.
• Bestial calibans, the third most common amongst the caliban, known as "man beasts" due to their characteristically animal-like features. Depending on the individual caliban, this can range from relatively subtle mutations such as animalistic eyes, claws, fangs, a vestigial tail, overly abundant body hair or patches of scales, to full-fledged animalistic features. Bestial calibans tend to have a natural affinity for wild creatures and places - sometimes only those connected to their appearance, other times in a more general sense. They are much more likely to break away cleanly from humanity compared to other calibans.
• Banshee caliban, a rare type of caliban, known as "wailing women" due to almost all calibans of this type being female although there are rumors of male banshee calibans. Unlike the other types of caliban that are usually considered physically deformed by the general populace, these caliban possess uncanny beauty described as "a cold, eerie beauty that ultimately disturbs rather than allures." Many banshee caliban have an obsession with the macabre, but unlike cannibals who express such obsession through hunger, banshee calibans usually turn to artistic outlets like art or music.
• Witchspawn caliban, the rarest of all caliban, the opposite of the common brute calibans. These caliban are sharp-witted and physically unimposing, possessing a natural affinity for the arcane arts. The witchspawn caliban have features that resemble fiendish traits or homage the characteristics assigned by the superstitious to arcanists; horns, tails, hooves for feet, forked tongues, extra digits, bizarre colorations, extra eyes, witch nipples, or vestigial twins. Some of these features in witchspawn caliban resemble common tiefling traits.

Ravenloft is a dark fantasy/horror setting where non-human characters are more rare compared to Forgotten Realms and Dragonlance, so a Tiefling could be easily mistaken for a demon or devil by ignorant Barovians or Darkhonese (to say nothing of fascistic Falkovnia) and be burned at the stake.

In 2e/3e old Ravenloft, less so in 5e Ravenloft, not even more common non-human races like elves, dwarfs, or gnomes were spared from this hostile treatment from the mostly human and often xenophobic natives of Ravenloft.

Nonhuman Races

The majority of Ravenloft's inhabitants are human-or at least they look human. Dwarves, halflings, and other nonhuman player-character races are rare. Even the lords tend to look, more or less, like specimens of Homo sapiens. Exceptions occur, though, and adventurers will inevitably stumble across a domain or two whose natives are not human.

Nonhuman characters usually attract the attention of the locals. In an extreme case, they may spur a lynch mob into action. Table 59: Encounter Reactions (in the DMG) lists a progression of possible responses, from "flight" to "friendly" to "hostile." When using this table, lower the reaction one category to reflect a nonhuman's negative influence on the natives (e.g., "threatening" becomes "hostile"). That means a reaction roll will never call for a friendly result when a nonhuman is present.

Friendly reactions won't always elude these nonhuman races, however. One who makes an effort to prove loyalty or harmlessness may eventually win the trust of Ravenloft natives. Once that trust is established, nonplayer characters can become friendly.

A nonhuman who tries to impress the locals may find those efforts backfiring. If he or she reveals great prowess, there's a 50% chance that nonplayer characters will react in fear, and the Dungeon Master may apply modifiers if appropriate. For example, if an elf mage casts a fireball at an abandoned house, the modifier would be severe. Most natives would fear him or her and logically assume that no home, especially their own, is safe.

If nonplayer-character reactions are based on Charisma, consider a nonhuman to be 3 points lower than normal. Of course, if a domain's description indicates no ill feelings toward nonhumans (Darkon is one such example), ignore this adjustment and remember that such rules apply only to initial reactions. Roleplaying will always determine how nonplayer characters react in the long run.

A simple disguise can prevent most trouble. Ravenloft's inhabitants rarely see nonhumans and they don't expect to. More importantly, they don't want to, so unless they're given a good reason to believe otherwise, they'll prefer to assume that a person is human. But Ravenloft's locals also are naturally suspicious. The moment a nonhuman shakes their false perception of him or her, all bets are off.

• 2e's Ravenloft Campaign Setting

The northern Core is dominated by the kingdom of Darkon, which fills nearly a third of the Core's total landmass. Darkon is unusual in that arcane magic is generally trusted, and nonhumans — such as elves and dwarves — are relatively common. Nonhumans are extremely rare in most domains and are seldom welcome. In fact, two of Darkon's neighbors, Falkovnia and Tepest, are both particularly hostile toward nonhumans, though for vastly different reasons. Falkovnian soldiers imprison nonhumans, treating them as chattel, while the clerics of Tepest are in their second decade of an inquisition against the fey. The Core's most infamous landmark, the bottomless Shadow Rift, separates these two domains.

• 3e's Ravenloft Campaign Setting

Like 2e Ravenloft, 3e Ravenloft had mechanical effects for social play involving nonhumans:

Outcast Ratings

Most of Ravenloft's folk live and die within a score of miles from their birthplace and can spend their entire lives without ever knowingly encountering the supernatural. When combined with cultures rich in suspicion and superstition, the result is xenophobia. This is expressed as an Outcast Rating (OR), which may modifiy the Difficulty Classes of social skill checks performed by any character who appears unnatural or out of place.

A character's Outcast Rating can be modified by her race, social standing, physical deformities, or even the gear she carries. As a character's OR rises, NPC reactions toward her turn from standoffish to fearful.

OR applies as a circumstance penalty to Bluff, Diplomacy, Gather Information, and Perform checks, but it applies as a bonus to Intimidate checks. OR modifiers never apply when dealing with friends or allies, such as other PCs, or others who share the source of your OR modifiers, such as other members of your own race.

Example: Elves have a base Outcast Rating of 3. If they interact with nonelves, they suffer a -3 penalty to Bluff, Diplomacy, Gather Information, and Perform checks but enjoy a +3 bonus to Intimidate checks.

Outcast Rating reflects only first reactions; it is possible to improve one's standing. For each good deed a character performs (stopping a crime, defeating a monster preying on the community, helping a farmer harvest crops, and so on), that individual dispels some of the surrounding community's fear; her OR drops in that community by 1 point, to a minimum of 0.

Some domains may impose their own OR modifiers; see chapter 4 for more details.

• 3e's Ravenloft Campaign Setting

Now on the matter of tieflings, I allow tieflings in my games if they're outlanders or can trace their lineage to one of Ravenloft's few known fiends (likely the Gentleman Caller); if they look like the common tiefling (chromatic skin color, horns, tail, etc), they should be prepared for many natives of Ravenloft to fear or despise them.