Reading your quick analyses on the latest chapter made me wonder. Do you think there is any possibility that the facility in which Finny was held is also related to Undertaker?
German drug lab and Undertaker
That's highly unlikely... unless the drug tested on Finny was later used for someone like Polaris. Otherwise, it seems too broad of a scope for his attentions. Mostly, it seems too early for Undertaker to be interested in anything more than cinematic records and how to revive the dead.
Finny's experience seems too far removed from anything Undertaker was doing, and I don't mean physical distance. Undertaker could easily be up to something in Germany, as he definitely has something going on in France, but it's likely not drug testing, and even less likely for strength-enhancing drugs.
It would be interesting if Undertaker turns out to be the main person in the Osiris group... and he was just lying about being interested in drugs. Stoker definitely fell for his lie that all of this revival technology was purely medical science.
Even if Undertaker is with the Osiris group, I don't think they are particularly concerned with strength-enhancing drugs... unless, like I said, he finds use for it with bizarre dolls like Polaris.
It's important to note that none of the bizarre dolls on the ship seem to have much strength. Finny was dosed with whatever for an extended amount of time, and he's the first to join the Phantomhive household after Sebastian. By the time the "animal weapons" are set loose on the ship, Undertaker should have been able to get them all dosed, especially if he told Stoker the drug would help with the revival process. It wouldn't have been administered over a long time for them, but it would be a somewhat fresh dose.
Undertaker comes up with all sorts of ideas, based on various information and his own observations. Even if he later uses strength-enhancing drugs on bizarre dolls, it's probably technology he took... not something he helped develop.
I'd look at the German military. Maybe Diedrich knows something about it, much like he found and pulled the top secret files about the witch project. He might have helped our earl on that drug testing facility, too.