I guess Mattie is being allowed to use her body by Erishkigal but isn't fully there, kind of like a puppet. That makes me ask why the grave dust bothered her since the earlier conversations implied she wasn't really all there. It was all very murky and unclear what's up with Mattie.
The talismans weren't explained much better, were they? From the early episodes when they got that book, I recall the Summerian gods used them to bind Inanna in a human form. I suppose that limited her powers from her full goddess form? I guess the anglerfish in s1 was keeping her from opening these gates and the board all had control of the Talismans, one for each of the four. Nothing really foreshadowed this in s2 that I recall and I wonder if the story seems messy because the writer didn't really have this well plotted out?
I guess the Dean would want the talismans because she could use them to free herself from the human bonds trapping her? I don't see what the gang wants them for since they've done their job of binding the Dean. Do they want to bind her more? Get rid of her? To where if so? Kill her? There's nothing that sounded like the talismans were made to kill the Dean so I don't know what Laura's crew is really hoping to gain with them. Sure, I get the free Perry part, but then they have Inanna loose to deal with. I am not sure what Laura's play is supposed to be here.
I suspect s2 and s3 weren't really well planned out. Jordan Hall, the writer, and the producers may have had some idea for a longer story back when they made the first season but they and the sponsors had no idea how popular the show would be. Season 2 tried making a large mythos with varying degrees of success but the long hiatus before s3 makes me ask whether they were assured of getting a third season after s2 which was much less popular with the fandom before its end.
Breaking up Hollstein, killing Mattie, and then Danny, the convoluted story, all of that took a toll on the show's popularity. It's still widely successful for a webseries but they have clearly gone back to a lighter s1 tone this season. The story, though, remains full of plot holes and I think it's because Jordan never had the mythos she wanted locked down clearly. If older vampires are stronger as said in s2 why is Danny stronger than Carmilla? Is Mattie back or not? If Papa Hollis is worried about the kids why aren't all the families and the Austrian government involved, yet? What's the deal with The Board and the Talismans? There's a lot that doesn't hold up to the barest scrutiny and makes the story very messy. If Natasha and Elise were not so much fun to watch playing Hollstein, I am not sure I would have gotten far past s1.
I find it best to ignore the plot and focus on them. The story really isn't very well thought out to my satisfaction so it's easier to roll with the strange twists and eye roll and focus on the enjoyable parts which it still has a lot of.