FWIW, I thought of reskinning the Elf as a "Cambion" or Half-Demon.
Initially a Cambion looks human, but with every spell cast or every creature slain it gains one point of Corruption. After gaining each point, the GM rolls d100; if it's equal to or under the Corruption the Cambion sprouts a new demonic trait: horns, tail, hooves, glowing eyes, unnaturally colored skin, or some more bizarre mutation.
Cambions also have one positive(?) ability: when a Cambion even feigns anger, its dark heritage comes to the fore. Even a human-looking Cambion trying to intimidate someone can alter the Reaction roll by 1d3 points. Which way the reaction swings depends on the circumstances; some NPCs may acquiesce to a Cambion's demands simply to avoid trouble, while others may stiffen their resolve to fight such a foul creature.
If anyone's interested, I can dig up my original notes, but that's the gist.
Frank Mitchell
"The law, in its majestic equality, forbids the rich as well as the poor to sleep under bridges, to beg in the streets, and to steal bread." -- Anatole France