Innsmouth Horror introduces several new game concepts to the Arkham Horror Series, including Personal Stories unique to each investigator as well as the Innsmouth Look. The town of Innsmouth is hostile to the investigators, and they may well find themselves thrown in jail and fed to a Shoggoth while they search the town for evidence to call in the Feds. However, leaving Innsmouth to fester is a bad idea, since the Deep Ones will gather and rise, bringing with them the Ancient One.
Innsmouth Horror also adds 16 new investigators, eight new Ancient Ones, two new Heralds, Epic Battle cards for the new Ancient Ones, over 30 new monster markers, plenty of new encounters, and an expansion board featuring the town of Innsmouth. Over all, this expansion adds over 300 new cards to the base game.