As already mentioned by others, Adv. 2 started quite well. The "It" storyline was first introduced all the way back in Reynir's introduction in 2015, and supposedly Tuuri's death was necessary to advance its resolution. (And, I *guess*? To provide a reason for Onni to bargain with the Swan? Kinda? I guess we'll see.) That story was the impetus for Adventure 2; it had to be told.
There is the thinnest, barest, least satisfying pretext for Sigrun and Mikkel to be there. Part of the malaise of this Adventure was their presence. I love Sigrun & Mikkel as characters, but they seriously needed to go their own way. Even the new characters that were introduced spoke only to them, and this was not their story! Emil was easily written in to go along, he is not the problem, and a case could be made for Reynir chasing after Onni.
I admit that in the face of any troll they came across, we would all say 'omg I wish Sigrun was here' but the story would have been so much tighter with just the two (maybe 3) of them.
Except for the bears. I get that a BRIEF return just to see off Surma and the bears' storyline should happen, but yeah. With her cubs thoroughly dead-dead and no longer in need of her protection, you'd'a thunk she'd run off into the woods to mourn. Would a bear, even a beast bear, be capable of vengeance?
She had pacing issues in Adv. 1 too - she found herself needing to get the crew close enough to their pick-up point that they could walk there. However, they picked up the antagonists way back at the beginning point. So we had the spectre (geddit?) of ghosts following them doggedly for weeks in canon to get to their battle point, and then the plot had to twiddle its collective thumbs for two weeks to allow Tuuri's incubation period for the infection. Then there were two streams to follow, and thenwegottothepickuppointhooraytheend.
Now, where I agree with ScrimmyBingus, is that Minna didn't actually script Adv 2 out in advance as she probably had Adv. 1. She had some vague plot points to intersect - Onni goes on quest for Grandma, obtains Tuuri's assistance as a soul, Lalli & Reynir come to his aid to repay Onni's assistance when they were in Denmark, Grandma freed. Suddenly having to accomplish that, she had difficulties.
I think she had the idea for the Sentinel Mages and had figured out where to intersect that into the story. I think she had the idea for the Hotakainen backstory, but not the nuts 'n' bolts of how to present it. She came upon an interesting hook of presenting it as 'a time-travel dream that they all share!' which was cute but weird, especially with the bits that Lalli-the-child would never have seen himself. (note: the brief flash of anger Lalli exhibited at Emil 'it's happening all over again' - the flash of a fist against the garment - didn't happen in the flashback, sorry) I think Surma was not originally meant to be just a troll. I don't think she'd thought through exactly how or when Onni travels to Tuonela.
I think she orignally had a plan for why exactly she needed Tuuri to be dead to accomplish Onni's goal, hence the insistence for years beforehand that Tuuri's death was crucial for the plot. I don't buy that it was crucial to Onni getting the cojones to go on the quest, for Tuuri to be dead and no longer needing his protection. But I think that perhaps Minna's burgeoning faith caused her to have second thoughts about Onni's plan (perhaps involving dark rites that would make a Christian uncomfortable?). For what actually happened in canon, Onni's dead father or uncle would have served the purpose just as well as Tuuri, maybe better.
Any of us who have written long-form fiction get to that point where you don't know quite what to do to get from point A to point Z. You know all kinds of cool stuff that happens at point Z, but you also know that you can't just go there in the second chapter, the end. I postulate that Minna believed herself committed to telling a story she was no longer mentally committed to, and did not seek objective advice on the matter.