Spellscar
Spellscars are a kind of chaotic magical trait that a being can pick up after being exposed to the Spellplague and surviving relatively intact - more heavily mutated survivors are called Plaguechanged instead. Whilst it can and often does physically manifest as some kind of scar or unhealing injury, it's not impossible for a spellscarred individual to look perfectly normal... until they tap the power granted to them by their spellplague, which causes them to manifest some kind of aura of shimmering, unearthly blue flames. This can be, quote, "jagged cracks of blue light racing across the forearms and hands, a corona of azure flame, a blazing blue glyph on the forehead, or even wings of cobalt flame", amongst other manifestations.
Introduced in Dungeons & Dragons 4th Edition in the Forgotten Realms Player's Guide, spellscars are a kind of prototype to the "combat theme" that would later appear in the 4e Dark Sun, being a collection of cool attack and utility powers that a player can choose to represent the unearthly abilities that their character's spellscar has given them. However, being a spellscarred requires using the 4e multiclassing rules, starting by taking the Student of the Plague feat, which grants the player one of three minor benefits as well as the power to use the Novice Power, Acolyte Power and Adept Power feats to take Spellscar Powers. They also have a unique Paragon Path in the form of the Spellscarred Savant, rather than using the normal rules for Paragon multiclassing.
Being a spellscarred comes with some benefits and drawbacks. Aside from the potential individual traits of Student of the Plague (darkvision 1 square, grant yourself +1 Speed as an Encounter power, grant yourself +1 Reach as a daily power) being a spellscarred grants you the ability to detect spellscarred, plaguechanged and pockets of spellplague within 5 squares. The downside? You suffer a -2 penalty to all defenses and saving throws against spellscarred or plaguechanged creatures, and against hazards caused by the Spellplague itself... unless you take the Spellscarred Savant paragon path, in which case your penalties turn into +2 bonuses instead.
Canonically, spellscars all vanished from the Forgotten Realms after The Sundering, as Mystra restored the Weave and so purged the last of the Spellplague from the world.
Spellscar powers all tend to revolve around fire, magic, and creepy ass mutations. For example, distending your jaw into a gaping inhuman maw lined with teeth of sapphire flame and then biting somebody in half, or having your blood emerge from your skin, crawl up your blade into a guy's wound, and siphon off some of their life force to heal you.