Thanks for the good feedback so far
For this you need to create the following 8 combinations in ONE playthrough. It is listed below from most to least common item drops. Chem/Strong Chem Fluids are pretty plentiful in supply.
Chem + Herb (plentiful and easy to find/make)
Chem + Gunpowder (plentiful and easy to find/make)
Chem + Solid Fuel (somewhat limited, but loads in Old House)
Chem + Supplements (for me, supplements were very limited. See below.)
Strong Chem + Herb
Strong Chem + Gunpowder
Strong Chem + Solid Fuel
Strong Chem + SupplementsThis is possible on any single playthrough of the game, be it your first or last, but it must be in ONE. The achievement is non-cumlative. I got 7/8 and had to do it on a later playthrough because of the one playthrough I missed.
I recommend you do this after
your speedrun (either on your madhouse playthrough, or if you are doing a 3 Med kit / 3 Item Box run separately). This is because completing the speed run will give you Xray Glasses, which point out every single collectible and item you can possibly pick up. Check everything, and you can't possibly miss out on any ingredients.
I did this on my madhouse / madhouse coin run, so this is obviously entirely possible, but items are in more plentiful supply on easy/normal.
For those struggling with Supplements, which is the only ingredient people are consistenly finding less than at least 2 of, there is one in the Testing Area where
and 1/2 on the ship during
on (I believe) all difficulties
(or at least for me).