Orpheus is a vampire drug, a mystical opiate which is taken in with the blood of those they feed from – the humans typically inject the drug into their bloodstreams before the feeding.
The enchanted drug can be easily tasted on the blood, and its effects on the vampire are very quick, especially if the dose is large. Of course, a dose that large will tend to knock out the human, leaving them in a comatose – and potentially fatal – state.
Smaller doses can be euphoric for both parties, but larger ones induce what can only be described as a vision quest, in which both parties travel through the history of the vampire in question, and choices made along the way determine whether either of them ever wakes up again. This experience of taking the drug has been described as being taken to Hell and left there.
Related Drugs: Black Frost, Calendula, Calynthia Powder and Gill Man DNA.
Another fairly natural fit: Buffy’s shadowy government manipulators and those of Delta Green work very well together. After all, both groups fight the monsters in the shadows while struggling not to become more like them, and both groups prefer to operate in secrecy.
Calynthia Powder is a bright purple colour. As a powder, it can be mixed into liquids and ingested, such as water or blood.
The drug is presumably magical in nature, and is used to affect the dreams of the person being fed it – usually without their knowledge. The drug makes the user more suggestible, especially when in a dream state, allowing anyone present while the user is dreaming to plant suggestions in their mind – while full control is not possible, it can be used to manipulate the person.
A person under the influence of Calynthia Powder will sleep more deeply, which makes the manipulation easier, as they will not wake when they otherwise would. Repeated doses will upset the sleep cycle of the user, making them sleep longer, dream less and awake less refreshed.
Related Drugs: Black Frost, Calendula, Gill Man DNA and Orpheus.
There are certain works that many would consider to more crossovers with the Buffyverse, but personally, I think of these three as implicit within it. Each of them has good reasons for being considered canonical in-universe, despite not being officially a part of it:
Not only is this a fairly obvious one, I’m still absolutely astonished that I never did a Buffy crossover with anything before. You can bet I won’t allow that state of affairs to continue.
Calendula is actually a real substance: it’s a herb derived from the plant of that name. The plant is a small yellow flower that grows across Mediterranean Europe and the Middle East, from the Azores to Iran.
It actually has medicinal effects – it has traditionally been used to treat constipation, abdominal cramps, acne, and in modern eras, radiation dermatitis and tumours. It is also used in cooking.
What lands it on this list is its supposed magical power: it is used by some members of the staff at Wolfram and Hart as a means of cheating psychic scans, by allowing users to hide their true thoughts and feelings.
Related Drugs: Black Frost, Calynthia Powder, Gill Man DNA and Orpheus.
An alchemical concoction masquerading as a beer, Black Frost was briefly on sale at one particular bar on the Sunnydale campus of the University of California.
Repeated doses of Black Frost will lead to the imbiber reverting to a caveman-like level of intelligence, closely followed by physical mutations to match. Understandably, the user rarely realises that they have been dosed before it’s too late for them to realise much of anything.
It’s mostly used to get even with smart-ass college kids.
Related Drugs: Calendula, Calynthia Powder, Gill Man DNA and Orpheus.
Gill Man DNA is a powerful mutagen that is incorrectly believed by its creator to be a steroid.
Ingested in the form of steam, Gill Man DNA is derived from mutated fish DNA, itself engineered from several different fish species and then further warped by exposure to the magical energies of the Sunnydale Hellmouth.
Although it does increase the swimming abilities of those who take it, the manner in which this is acheived is by slowly mutating them into amphibious fishlike humanoids (it is not clear whether they can breathe underwater as well as in the open air).
Related Drugs: Black Frost, Calendula, Calynthia Powder and Orpheus.