Blood on the Altar, The Dunwich Legacy Mythos Pack 3
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This product is a Mythos pack.
All Arkham Horror The Card Game LCG expansion require the core set to play.
Stand alone scenarios can be played on their own like the name implies but can also be added into any of the campaigns. They're nice filler if you're on the current campaign and the next pack hasn't come out yet.
Big box expansions are the first in a series of expansions. Each one has 6 mythos packs linked to it which complete a campaign.