Doppelganger Potion, alternatively translated Doppelganger Medicine, is one of the magical potions first described in Monster Girl Encyclopedia I and later in Monster Girl Encyclopedia World Guide III.
Book Information
Doppelganger Medicine; MGE1
Magical Medicine: Male Targeted
Once a monster girl recognizes a man as her husband, she'll no longer want sex with anyone else but him. This magical medicine was developed for them, so they can enjoy being gangbanged and raped by lots of men even with just their husband. It's used by having the man drink it, and when he does, it causes a separation of spirit and magical energy. Depending on the amount that is imbibed, 2~10 identical looking doppelgangers can be produced. The doppelgangers aren't just doppelgangers. They're all the man himself, and he shares the sensations of all of them collectively. He undergoes a sensation like having all of their feelings sent into his head at the same time, while moving his body at the same time. Of course, even if it's an incubus, this sort of thing throws the mind into chaos. Having sex in this state amplifies the pleasure experienced by many orders of magnitude. For that reason, men who drink it lose all rationality and thinking capability. The more dopplegangers there are, the more the man transforms into a mindless, bestial rapist. The monsters are extremely happy with the result, and since the doppelgangers are all the same man himself, their penises have the same taste and shape as their beloved husband's, and they all shoot sweet cum that's exactly the same as their husband's. In spite of pair bonding, monsters can enjoy being thoroughly and mercilessly gangraped by many mindless husbands who have been reduced to beasts.
Doppelganger Potion; Sabbath Grimoire
A liquid potion with a mysterious color of blue and black continuously mixing and separating, which temporarily creates doppelgangers of the one that drank it. After they acquire a male that becomes their partner, monsters only join with their partners, but this was developed for the enjoyment of "gangbangs by multiple men" with only a married couple. A human male drinking it causes symptoms of mana separation to develop, and can usually produce 2 to 10 doppelgangers depending on the amount drank.
On the surface, it appears as though the person that drank it multiplied as is, but that does not mean the "existence" of the drinker increases. That is, even though they are called doppelgangers, the consciousness, thought, and soul are whole without increasing, and all of the doppelgangers are commanded by one will. In short, rather than increasing one's self, it is a sense that they can move more of their body, it seems to be a feeling partly close to that of "tentacle potion" which feels like "the limbs have multiplied". For that reason, although each of the doppelgangers can be moved, that doesn't mean each has a separate intention, so there is no such thing as a split opinion or quarrel between fellow doppelgangers.
Also, since the doppelganger is not just an illusion, but a man's body itself, it is possible for all of the doppelgangers to use that body's physical and magic abilities. The visual, auditory, tactile, and pleasurable sensations that all of the doppelgangers receive is brought to one base consciousness, and is shared by all of the doppelgangers. In other words, the man that drank the doppelganger potion will move all of the doppelganger's bodies at the same time, and have the senses of many people simultaneously received from all of the doppelgangers sent into just one head. Of course, it is next to impossible not only for ordinary humans but also for incubi to control them all at the same time, and in many cases the head becomes confused and unable to understand reason, making rational thought and decisions impossible.
As the number of people increases, it becomes impossible to think of anything, and the doppelgangers begin to move very impulsively based on instinct. In other words, if a monster companion tempts them in this state, the doppelgangers become an existence meant only to rape the monster before their eyes, and will swarm the woman's body. Naturally, men will become further reckless from the pleasure received from numerous doppelgangers, and from each one's thrusting penis, their ejaculations, and their essence being spewed out, it brings great joy to monsters to be surrounded and overrun by their beloved.
Basically, it is a potion for human men to drink, it is not recommended to let monsters drink it. That is because, as we know, the desire monsters direct towards their spouses is an unusual thing, and even if it is only one monster, they are beings that pour enough lust and pleasure to nearly drown a man. Therefore, if such monsters multiply, and impulsively move to rush a single man, the man will be assaulted by an overwhelming pleasure of unfathomable degree. It is unknown how much will be squeezed out before a man loses his mind, or even how much will be squeezed out after he has lost his mind, but for a man with a defiant heart, perhaps it might be nice to give it a try.