The ??? mixture is an item that can be obtained during Recruitment Drive. It is made during the Miss Cheevers challenge when ingredients are mixed together incorrectly. There are three ??? mixtures obtainable during the quest, none of which are useful in completing the challenge. Because many of the ingredients cannot be retrieved after use, it is likely that the challenge must be restarted if a ??? mixture is created.
The hot mixture is made by using cupric sulfate on the vial of liquid. The horrible mixture is made by then using Acetic acid on that mixture. The warm mixture is made by using gypsum on a vial of liquid.