Miasmic Rush was an Ancient Magicks spell which required level 61 Magic to cast and could do a maximum of 180 life points per spell. In addition, any player either Melee or Ranged style weapons would have their weapon speed halved for 12 seconds. As with all Ancient Magicks spells, the quest Desert Treasure had to be completed to cast this spell. The spell also required Zuriel's staff or its corrupted variant, making it one of the first Ancient Magicks spells to require more than just runes to cast. Despite only requiring 61 Magic, the standard Zuriel's staff required 78 Magic to wield, making the corrupted version the only viable option for lower levelled players.
As Zuriel's staff degrades over time, an extra 9,041.8 coins should be added to the cost of each spell (assuming the non-corrupt version of the staff is used) for a total of 9,789.8.
The word "miasmic" comes from "miasma", an Ancient Greek word meaning "pollution" or "bad air" which referred to blood pollution from killing those taking shelter in a temple, or killing family. It was also the non-existent gas believed to be responsible for plague and other diseases in 1700s Britain; plague was more due to vermin like rats.