To unlock extra characters, complete the requirements and buy them from the Costumes area of the collection screen.

• Peter: Beat the "Decisions, Decisions" Scenario on Hard Mode.
• Greg: Beat the "Decisions, Decisions" Scenario on Very Hard Mode.
• Fireman: Beat the "Hellfire" Scenario.
• Frank: Beat the "Decisions, Decisions" Scenario with George.
• Monica: Beat the "Below Freezing Point" Scenario with Yoko.
• Yoko D: Beat "Outbreak" with Yoko.
• Bob: Beat "Outbreak" with Mark.
• Will: Beat "Outbreak" on Very Hard Mode.