Biohazard is a loving homage to a genre recently finding newfound vigor, the zombie apocalypse. Players take control of members of a Special Forces team inadvertently isolated and surrounded by swarms of mindless machines of death. Despite this, they have a mission, which they must succeed at to save the human race. Right from the introduction, there is very little preamble and the mobs of undead attack within minutes. Unlike other modules, there is little variety of monsters (only five) and most of these involve dozens upon dozens of minions which appear endless in their attack.
The first encounter presents four of the larger infected drones and swarms of minion grubs. Further battles increase this number, changing the environments from an open street and inside houses to finally a last stand atop of an evacuation point.
Don't be afraid to go over the top, detailing the carnage and the colorful ways the infected meet their end. At the end of this module are the five pre-generated characters using the classes presented in the Amethyst: Foundations core rulebook. Distribute these to the players and allow them to get comfortable with the role and whatever personality they wish to apply to them. Encourage camp and overacting. Persuade players to make inappropriate jokes, snide remarks, and one-liners after a particularly colorful kill.