- Self-Imposed Challenge: New "Taboo" rules. Their purpose is nerfing overpowered or overused cards and abilities (for example, "Machete" now cost two experience points to purchase, but still counts as level 0 card, and Rex's reaction ability works only once per round), and buff useless ones (like "Springfield M1903", which is now cheaper). Players must chose to use or ignore "Taboo" list in its entirety, they cant just use parts they like and ignore the rest.
- "Return to..." expansions add additional rules, called "ultimatums", to make game even harder. Ultimatums are the same for each expansion, and are completely optional to use; players are free to use expansion content without adding any of them.
- Besides ultimatums, each "Return to..." expansion has list of achievements; some of them generic ones, like finishing campaign on hardest difficulty, but most are campaign-specific. For example, Return to the Night of the Zealot expansion has "Interrogate all unique cultists in Midnight Masks scenario", and "Complete Night of the Zealot campaign without killing any ghouls".
YMMV / Arkham Horror: The Card Game