Dark magic is a destructive force that draws power from the oldest and greatest of emotions; fear. A dark mage cats their spells from a mirror, which holds the fear and turns it into dark power. The simplest spell is to release all the power within the mirror at once, in a burst of destruction. It is similar to an explosion, but for the lack of concussive force or fire; the black burst simply obliterates anything it touches. With practice, the mage usually learns precision and control, enabling them to mete out energy and utilize it more efficiently, perhaps focusing the release into a narrow beam with longer range or multiple projectiles.
To gather their power, a mage must gaze into their mirror and focus on what frightens them. This perverse form of meditation will never seek to overcome or learn to live with these fears, for if they do so then power will be lost. Instead, mages simply fixate upon their fears and paranoia, warping their minds and twisting their souls over time.
There is no upper limit to how much fear a mirror can hold, but the more it is given, the harder it will be to control. Like filling a wineskin, it can stretch but will start to leak, and when you pierce it the contents may come gushing out when a more controlled stream might have been preferred. Mirrors will also leak when left idle for too long with power inside, becoming tarnished and shadowed. It is for this reason that most dedicated mages will keep a polishing kit along with them, as it takes much more focus to use every iota of darkness each day than it does to simply clean the mirror regularly. Some say that when a mirror is completely consumed by this darkness, it changes into a new metal, a black silver that has special properties. There isn't much evidence behind this however, and the mages themselves are unwilling to confirm or deny these rumors.
Most dark mages either come from or were trained at the white palace. Built of polished sandstone, it lies near the edge of the northern desert. The entire building is white, so that no dark magic can be hidden there; despite their many powers, no dark mage can create light. They are paranoid, distrustful, and violent people overall, and there are plenty of stories involving an unlucky traveler or villager being slaughtered for any small slight or even nothing at all.
The order of Light’s Shadow comprises the largest organized group of mages, though organized seems a stretch. They control the white palace, using it as a meeting center as well as a place for training new mage apprentices. They currently work with the kingdom of Orisria, centered in the jungles to the south of the desert. This is how they have access to the fine silver used to make their arcane tools, though the specific power structure of the order is quite hard to pin down due to frequent backstabbing and mysterious deaths.
Seppam the gnoll is a dark mage from the deeper deserts, near the famous volcano of the sands, who uses a mirror of obsidian. Some say her mirror can hold more power than others and never tarnish, but she is not part of the order, and refuses to share her secrets.
Sir Markim is a knight errant who is rumored to be a dark mage, though he does not carry any mirror openly, or keep a polishing kit. He’s even known for using a spell that creates a sword of darkness, but mages look down on personal combat as brutish and needlessly hazardous, while most warriors see mages as weak and paranoid, so it’s unlikely that someone would put the two together.