Half of our group is moving across country, so we've decided to wrap our Strange Aeons game with the conclusion of "In Search of Sanity." I'd like to pay off the amnesia plot point, but I'd rather avoid shelling out for Part 2 of the AP just to get that information.
So can the community help a GM out with some specific spoilers? Why did the PCs lose their memories?
As a secondary request, if you have any thoughts about interesting ways to pay off the Count Lowls storyline as a truncated campaign finale, I'd appreciate the assist there too. (At the moment I'm leaning towards "they fight him in a level-appropriate version of Carcosa while he's doing something nefarious with his book.")
As for the final encounter, your idea is not bad. He is quite a bit ahead of the characters in the actual storyline, but you can have him run up against obstacles that allowed the characters to catch up with him.
While I do think it's a shame to run Strange Aeons without doing Dreams of the Yellow King, the campaign's story is ultimately simple enough that it can be compressed down to a few short encounters and brought to a swift end at almost any junction. The fact that much of the campaign occurs with the main antagonist "one step ahead" of the PC's means you can end it pretty much any time by just letting them catch up.
Probably the best way to handle the PC's memories if you're ending in book 1 is to have the final battle against the Tatterman play out with echoes from the dimension of dreams appearing around them. Round-by-round as the PC's fight tell the story of how their minds were sacrificed.
Start with Lowls performing a ritual to take them to the dimension of dreams, lead them towards the Mad Poet, and then murders them there in the dimension of dreams. While this still leads a plethora of unanswered questions, it does pretty communicate the gist of the situation. It can also make clear his plans: the Mad Poet gives him the Necronomicon directly and with it the ritual to activate the Star Stelae and enter Carcosa, drawing in all of Thrushmoor with him.
This then allows you to have the PC's rush his mansion (remove most of the cultists; you're not running book 2 in its entirety, and just want to move towards a final confrontation as swiftly as possible) and confront Lowls as he attempts to complete this ritual. They can find evidence of their past lives both in Thrushmoor and the count's mansion, further adding to their past. There's also something wonderful about a final boss showdown occurring during a dark ritual.
Lowls himself should probably be an aristocrat; he's a perfect opportunity to create a villain with no special powers other than having a lot of money to throw around, and given the PC's level range at this point this is a believable and satisfying opponent to end the campaign on.
** spoiler omitted **
Cheers! I can easily switch "evil entities" around and do some transplanar encounters. Should be fun.