The free sample potion is a drug-like liquid potion used by Stan Pines as a last ditch effort to make the unnamed traveler pay for not buying anything in the Mystery Shack.
History
Sometime before the events of "Little Gift Shop of Horrors," Stan somehow obtained or made the drug with the specific intent to knock out anybody who drank it, saving it just in case a situation that would require it would happen.
Near the episode's end, Stan, who is upset that the traveler hasn't decided to buy anything, offers him a "free sample." The traveler accepts and drinks it, and then experiences a sudden sense of vertigo before falling unconscious. Its sleeping effect lasts only a limited amount of time, as the traveler wakes up to find himself encased in a glass box.
Appearance
It is a bright green liquid substance kept inside a glass test tube. The potion is almost identical to the voice-altering tonic that Dipper drank in "Bottomless Pit!."
Sightings
Season 2
- 206. "Little Gift Shop of Horrors"