I'm also planning on running Masks as the next campaign for my gaming group. We just have to finish off the AD&D 2nd edition campaign were currently running, which should take another 4 or 5 sessions.
I've read the advice here and in a few other areas including the link that Ross posted.
My gaming group including myself has never played Call of Cthulu. I'm planning on running a scenario to introduce Jackson Elias and to help us all familarize with the rules before we jump into Masks. I'm thinking that I would prefer this scenario not get too deep into the mythos though. I don't mind cultists and the like, but I would rather have the group not knowing that the mythos or the supernatural does exist until they encounter it during the Masks campaign.
I guess I just need a good detective story to get Jackson introduced and keep the Mythos hinted at instead of confirmed.
Any thoughts or ideas about the introduction or advice in general? I will be a rookie Keeper running a bunch of rookie players so I'm sure I can use it
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Marik