A prototype version of Sway Venom that, instead of the expected infection related to Shadow Kraata infecting Matoran, killed the subject. It was used on Iano and Axizx, before the makers used actual Kraata Slime, to perfect its true purpose.
Electrax also was injected twice with this, but it didn't do anything to him.
It is also a food that fed Shadow Bats, which were immune to the poison. Mad scientists in Metru Nui kept some to feed their Shadow bats, which gave them supplies.