the most important thing first: Laurence is the most misread character in Bloodborne, possibly all of soulsborne in general. He is the prince of Cainhurst and the Child of the Vilebloods, not a random ambitious man who studied at Byrgenwerth and f****d up. His body is female, while his head is male. He does have fully functional female biology, can get pregnant and carry children, but his dangerous blood makes all of them die. The game story is about the attempt to save one of these children, fathered by Gehrman the First Hunter, from death upon birth and about the events caused by this attempt.
Gehrman's Lost Leg [WIP]
Bloodborne infection, the Burial Blade, and the Nightmare Frontier
Gehrman's amputation
Gehrman's missing leg is not cosmic sacrifice or mysterious price paid to the Moon Presence.
It is the medical consequence of intimacy with a fire-carrier whose unrefined blood is the scourge itself.
The Orphan of Kos (Gehrman's manifestation in the Nightmare) wields a blade (visible underneath the placental tissue) based on a knife used to cut flesh around a bone before amputation, possibly implying that Gehrman might have done this with his own hands. The Burial Blade, when not transformed into a scythe, has this shape as well.
In pre-antiseptic, pre-anesthetic times, amputation was an awful thing to suffer through, connected to extreme pain and fear. Flesh had to be cut, bone had to be sawn through quickly while multiple people had to hold the conscious patient. It is no surprise that this could form a Nightmare and the affected nervous system could ascend into independent Amygdalae.
Beast blood crawling up the right leg is a conclusion people came to after seeing what happened to Gehrman. This is the origin of belts and straps worn around the leg. The Scourge represents a few things, including Syphilis. By being intimate with Laurence, Gehrman got infected, which first manifested in his right leg. However, it might express differently depending on the person, and certain hunters are extra cautions by wearing straps around both legs at once.
This doesn't necessarily mean they know how the infection happened in the first place or what it actually is - but the things they were able to observe created certain persistent beliefs in methods which may or may not work.
The Moon Presence (Flora) took Gehrman's leg as payment for the Hunter's Dream — a cosmic toll demanded by an unknowable entity.
correction:Flora did not exist yet when the amputation occurred. The leg was already gone before she was ever born. When Flora's essence later manifested as the Moon Presence and trapped Gehrman in the Dream, she was binding her father through grief — not claiming a body part as cosmic price. These are separate events connected through causality, not transaction.
After his leg was amputated, Gehrman forged the Burial Blade from his severed limb. The bone structure of the leg became the scythe's handle and blade — not arbitrary craft, but deliberate symbolic action. The weapon was intended to bury Laurence and Flora properly, and to fulfill their agreed vow: if Laurence's transformation progressed beyond saving, Gehrman would use it to end him mercifully. The leg lost to beast blood infection becomes the blade that would end the beast itself. Grief made material. Loss repurposed as the instrument of their promised ending.
The weapon wielded by the Orphan of Kos
It's hard to see in the fight, which is speedy and chaotic, but underneath the placental tissue, there is clearly what appears to be a curved metal blade.
Antique blades used for amputation. They are curved to cut around bone, removing flesh for the saw that comes afterwards.
The components of the Burial Blade
The blade of the Burial Blade shows the same curved shape again. When transformed, it gets connected to the leg-bone shaped extension that turns it into a reaper.
I have speculated that the Burial Blade and Blades of Mercy might have swapped names, but upon closer inspection this does not seem to be the case; the Burial Blade is literally supposed to bury Laurence. Possibly it was originally intended that Gehrman would fight Laurence's beast form.
The Nightmare Frontier
While the Hunter's Nightmare displays the tragedy of the attempted birth of Gehrman's and Laurence's child and the death of Laurence, the Nightmare Frontier displays the way towards that - the fear and terror Gehrman had to experience from the intimacy that led to Flora, and what it cost him.
The Nightmare Frontier is full of Gehrman's fear imagery, and the boss is an Amygdala, which is literally associated with fear. The main images that are reoccuring here is the vagina dentata as well as poison. This is the nightmarish exaggeration of a bloodborne infection through intimacy.
This does not necessarily mean Gehrman was afraid of Laurence or the intimacy itself, but he definitely was afraid by the time he realized he got infected.
The Amygdala as the boss of this area taking off its own arms might even imply that Gehrman performed the amputation on himself with his own hands, but this is highly speculative.
The Amygdalan Arm is also found in the Nightmare, in a cave on the way to Laurence's corpse, at the river of blood that likely is his.
Crawler in the Nightmare Frontier swamp area
The similarity of the Crawler enemies to Kos has been noted before. They represent a Vagina Dentata, a toothed vagina which took Gehrman's leg due to infection, which is why they also spit poison.
They also resemble certain manifestations of Nyarlathotep, which further ties them together with Oedon, whose living incarnation Laurence is. This is harder to see in the game alone, but very obvious in the concept art.
Silverbeasts have tilted heads with sharklike teeth in their mouths, which also resembles a Vagina Dentata, alongside them obviously being inspired by Gugs, a creature from Lovecraft's Dreamlands which is defined by their vertical mouths.
Silverbeasts are another dream symbol for Laurence. This enemy type even drops Bastards of Loran, which means they were pregnant with children that mummified, dried out and died inside them, a possible nod to the fate of Flora, if the Bastards aren't literally outright Flora herself.
The rock-throwing giants internally are called "lost children". They also have lots of cuts on their bodies, visible well on the back. It is possible that they manifest in this huge, crushing form because of the crushing guilt connected to the loss.
It's unclear where their cuts come from; one possibility is that it's a hint to the crude surgery which attempted to birth Flora. They somewhat resemble the Living Failures, which also are a manifestation of lost children. Both have strange semi-fluid looking heads seemingly with no neck, although in case of the Living Failures the neck could be covered by soft tissue.
I do not currently have anything further to say about the possible connection between the Lost Children and the Living Failures, other than them sharing similar features and both being lost children. The similarities are notable, but I will not invent explanations for the possible connection without further examination.