The next item on Dr. Kai's list of research goals was a sample of elven foot sweat. He had hypothesised that the hypnotic effects of monster boy feet were caused by a foul-smelling and volatile substance secreted from between their toes; a substance which, if there was any truth to the rumours of adventurers falling into a trance after mere seconds of exposure to an elf's soles, should be found in high concentrations in their sweat. Sadly, from what Dr. Kai could piece together, elves would only sweat voluntarily. This meant that, if he wanted to get any decent sample, he would have to bring a live elf to his laboratory.
Of course, this was easier said than done... on one hand, elves weren't exactly hard to find - unlike most races of monster boys, elves were social beings who could live for thousands of years, seldom leaving their giant tree-cities. This meant that, once founded, elven colonies would rarely be abandoned. And fortunately for Dr. Kai, there was one such colony only a few miles north of his town.
At the same time, hunting down an elf, particularly in his natural habitat, was a dangerous proposition. Besides the aforementioned allure of elven feet, elves had an innate connection with the forest and its dwellers. Their cunning and agility was unmatched in all of the known races. Even with the help of experienced mercenaries, capturing an elf was a tall order indeed.
However, the same traits which made elves dangerous foes in their home country, also caused some of them to leave the forest and integrate the upper echelons on the Monster King's militia, as frightfully pungent warriors and generals. There were reports that an army of beast boys led by a elven marshwarden would soon pass by Dr. Kai's region on their way to besiege Antiuck. Assaulting the general's guard would require even more hired swords, but at least they would be fighting in roughly equal terms.
Aaand there was one last option... although the monster slavers would mostly trade in (more or less) foot-obsessed human beings, they would just as frequently sell other monster boys and girls. There was a good chance that if Dr. Kai were to infiltrate a monstrous slave market, he would be able to find a suitable subject for his experiments.
With those options in mind, Dr. Kai got busy planning the historically unprecedented capture of a living, breathing, stinking elf...