Dark magic is a tier-3 aura that can be bought from the Loyalty Programme Shop for 42,500 Membership Loyalty Points. When activated, any damaging attack will have a small chance of dealing a corrupting effect. The base damage of this effect is the lesser of (corresponding damage-boosting stat + 1) * 15, and 5% of the monster's life points. Upon activation, you will do 100% of that damage, then 80% of it, then 64% of it, then 51.2% of it (295.2% total or 14.76% of the monster's maximum life points). This happens over the course of about 10 seconds, and the damage is counted as auto-attack damage. It does not carry over from one monster to another if the first one dies while under the effect.
As an example, Glacors have 40,000 life points. If you were using magic and had a Magic level of 95, your dark magic damage would be the minimum of (95 + 1) * 15 (e.g. 1440 damage) and 40,000 * 0.05 (e.g. 2000 damage), or 1440 damage. So your first hit would be 1440, then 1152, then 921, then 737. Using dark magic can increase damage output by about 5-15% in the long term, although this is highly dependent on the monster's life points.
This would also mean a significant boost in damage if one was using a wand+shield combo, more noticeable than dual wielding or using a staff.
It is activated for 1 hour and has a cooldown time of 3 hours. As with all auras, if the account using it is logged out while the aura is activated, the timer will continue to run out.
This aura was made significantly more powerful thanks to a Ninja Team fix on 24 March 2014. Previously, dark magic did about 98 damage on about 2% of its hits, making it fairly useless. Additionally, it didn't work on poison-immune monsters like Glacors and ganodermic beasts, because the damage was counted as poison. This aura was further updated on 26 October 2015, allowing it to work for any combat style.