Looking to get some ideas for single- or dual-faction decks to use to demo the game.
I have a core set, Secrets of Arkham, Order of the Silver Twilight, one each of the first-printing Summons of the Deep and Dreamlands asylum packs, and all but Murmurs of Evil from The Yuggoth Contract.
I would suggest that you go to a deckbuilder site like cardgamedb.com, or download nyarlazorbec's deckbuilder app and play around. It's really difficult to know and remember which cards came x1 in those packs, but you do have a decent card pool.
I'd recommend doing mono Cthulhu with either a deep one or serpent theme. Also a mono-Miskatonic nerd rush. These are just to have some samples of "pure" factions from both mythos and investigator factions.
The others I would pair thus:
Shub/Agency - this would be more of an "aggro" deck with big hard-to-kill dudes and direct wounding effects
Yog/Silver Twilight - this would be a combo-ey control build with lots of events and bouncing (sacrifice and destruction events, and return to hand effects)
Hastur/Syndicate - this would be a control build focused on character removal and struggle control (throw in all the exhaust, all the take control effects)