this is how to concoct poisons.

1.) when you find a new ingredient concoct a poison using just it. (fermalgahyde is kind of unique from other ingredients fyi and only extends poison longevity rather then make it different)
2.) once you concoct a single ingredient you get either 1- emetic, 2-neurological, 3-fear, or 4-mind control.
3) Now think of each type of poison made from a single ingredient as a number,
emetic = 1
neuro = 2
fear = 3
mind = 4

to achieve the poison type you want mix ingredients to equal that number.

so If you want to make fear poison you can either brew
a single ingredient that makes fear poison.
three emetivc poison ingredients = 1 + 1 + 1 = 3
a neuro ingredient and an emetic ingredient = 1 + 2 = 3

so on and so forth. now the ranges are not just single integeres so if you get three really pathetic emetic ingredients you may get neuropoison but this formula will hold for the vast majority of mixing (circa 90-95%)

also I could be wrong on how this works but some times when you concoct grenades you get super grenades that hit the entire room for a lot more then normal damage. I believe these are created when you use legendary or famous ingredients. I can't confrim this through personal experience only to say that I have created the grenades that were super duper on occasion but I could not recall what I used to make them.