I know that the Pit Mutagen still affects organic creatures like the Squids, albeit slower than biomechanical creatures, but why is that? What kind of effects might it have on, say, humans?
Since there are no humans in the BIONICLE universe, impossible to say for certain, but I would assume they would be affected the same way they would be by mutagens in our world.
Why does it affect biomechanical beings (and Makuta) so rapidly then?
Given that Pit Mutagen is pretty much just salt water affected by radiation emitted from the GSR, I’m assuming that biomechanicals mutate faster simply because they are native to the MU and are more attuned to the source of the energy in question.