Black slime extract now inflicts a disease that turns the victim into a slime after a short while instead of immediately turning them through the chem itself. This gives people a chance to call out over radio about what happened if they were the victim of a drive-by sliming. Likewise it gives them a faint hope of reversing the process with the cure, frost oil (in the code frost oil is hilariously toxic to slimes). Source of frost oil are botany and (irony) xenobio. The disease is fast spreading, and infected are likely to only have 30 seconds to a minute to find frost oil, but it's highly effective once taken.

On the plus side for xenobiologists this allows for them to place black slime extract in things (medibots, food) without it becoming immediately apparent to victims what's been sabotaged.

This disease cannot be spread in any fashion besides black slime extract. (Because that would be so hideously broken if it was transmittable)

The flavor texts for the stages are an allusion to nethack, where the process of getting slimed is much the same (http://nethack.wikia.com/wiki/Sliming)

One other feature of note: mutant slime people retain the old black slime extract behavior, getting slimed almost immediately after exposure. This means that you can replicate pre-pull black extract by creating a mixture of equal parts black and green extract.