To copy-and-past from Wikipedia:
"A Tiefling is a being whose lineage can be traced back to some degree or another to that of a fiend or demon within the Dungeons & Dragons universe. ...
"Tieflings have any of a number of features that reference (directly or indirectly) their fiendish lineage. These include, but are not limited to, horns located on their heads, pointed sharp teeth, extra fingers, cloven hooves in place of feet, tails, and unusually colored eyes. They exude a feeling of "evil" even though their race has become civil and no longer lusts for power. Many races distrust or outright hate Tieflings .... Tiefling villains often live up to this reputation, whereas player characters have the choice to abandon this stereotype."
I made this particular tiefling a Witch (one of the classes in the Pathfinder system). Although she definitely looks the evil part, I haven't decided if she is truly evil or just likes to fool people into thinking that with her outfit (note how in the second image her 'tail' is on the bed beside her; she wears it when out in public to accentuate her 'demonic' appearance ^_^)
I did several versions of the first image, mainly to play around with some 'water' effects on the spirit she is summoning from the pool.
I also did a brighter lit version of the second image, and am quite surprised on how different it looks. The one in the darker image uses lights that make it look like a moonlit night, and I kinda like the effect it gave to her skin (on which I applied a 'wet' look).
I may do more 'naughty' images with her later.