HITMAN World of Assassination

JayD101 is correct, it must be LETHAL poison. Author did say “kill” but it’s worth pointing out that this achievement isn’t necessarily tied to the Secondary Fermentation challenge for the gassing part, since that challenge does pop when using emetic poison.

100% can confirm HAS to be lethal poison for the gassing in the barrel room. I'd already used emetic rat poison in a previous run, and, that didn't pop the achievement after getting Don Yates to neck the poisoned 1945. Redid the gas with the lethal poison and it popped.

I think it's worth saying that even though the poison kills Dianna too, I still unlocked the achievement as the mission failed screen came up so it still counts.

Given how all other similar, three-challenge achievements didn't force you to fail the mission, I doubt they intended to have you kill both targets with the poison, they just made a mistake and didn't bother to change the achievement. I think they meant you just had to poison both with gas, so emetic or sedative poison would suffice and which would reflect the Secondary Fermentation.

I think this overcomplicates Secondary Fermentation. I got the mercenary uniform, then got Black's outfit, waited for the winemaker. Then went into the field, got the grapes, got the winemaker, started the tour.

Switched back to mercenary, cleared out the gas room. Back to Black, asked a question on the tour (grape press), back to mercenary and started going under to break into the wine room from underneath... and heard the tour group above me.

I had to race back to reroute, then start the gas. I didn't have time to get the wine and I guess I didn't have to (for this one specific challenge). Everyone died, and I restarted. I had already done the other two, so maybe that's a difference, but I almost ran out of time.

26:33 "Now we're going to use the poison that we created on the ventilation system here, but do not turn it on yet, instead..."

Actually, do turn it on, then go up to the security room, where you have an unobstructed view of the targets, and reroute the ventilation when they're in position. Using the poison, going up to reroute the vents, then going back down to turn on the system is just adding extra running around.

I've been trying to figure out if there's a way to do this without killing Diana. I brought an emetic poison syringe, thinking I could get her to excuse herself from going into the barrel room, but there's no prompt to use it on her. Shooting her with the tranquilizer gun causes a panic and cuts the tour short. I seem to remember having an emetic poison dart in my inventory before; maybe I'll see if its still there and give that a try.