Also referred to as 'Potion'. A classic staple of the Conversion Bureau, serum described here is none other than that used to transform a human into a pony.
The Ponification Serum is the liquid substance used in Conversion Bureaus which causes the appropriate reactions in humans and initiates a metamorphosis into ponies. Its process is (to the public) unknown (mainly because the only information most Conversion Bureau staff and officials will disclose is that it was formed using a combination of human technology and magic).
Theoretically, the metamorphosis has a 100% chance of resulting in a convertee of the subspecies of Earth pony, Pegasus or Unicorn, but anomalous results have occurred in less than 0.0001% of conversions.
Such results include 'failed' conversions (detail is not permitted to be disclosed, but does not include death (hence it is a different point in this list)), death and, on one emergency occasion, a 'Code Majeste', in which the subject was converted into the Alicorn subspecies.
For the latter case, the Princesses Celestia and Luna were required for assistance in handling the convertee, the fate of whom is unknown to those outside of Equestrian Royal members.
The serum is generally described as a deep purple liquid with a slightly thick texture, rather like unset jelly. It smells and tastes of grape-juice. It can reportedly have small sparkle-like material inside, but it appears to vary.
Depending on the story, the serum might be injected via needle, or a potion to drunk. The amount of serum required to transform also varies. In some, even the slightest contact with human skin might prove enough for it to be effective in it's purpose. In others, low enough doses directly ingested might do nothing at all.