last quest in the road darkens
Ranger spikes: Yes, should attach. I don't see any reason not to, since the hero who gets Fallen Into Evil becomes an 'enemy' card type. You can still remove Fallen Into Evil with the usual Condition removal cards, and at that point Ranger Spikes will remain attached to the hero and just do nothing.
About resolution of the quest card effect... the first part is straightforward (remove Frodo, treat enemy engagement as 0, skip the travel phase). For the next part, just follow these steps:
At the end of the refresh phase:
1) Shuffle Frodo's Choice and Seat of Seeing into the encounter deck discard pile.
2) Now put the whole encounter deck discard pile on the bottom of the existing encounter deck (no additional shuffling).
3) In turn order, each player chooses a stage 3 and goes to their own staging area with that card. This staging area is empty at present.
4) In turn order, each player chooses one card from the existing stage 2 staging area, and moves it to his new stage 3 staging area.
5) Repeat step 4 until there are no cards left in the stage 2 staging area. Then, discard stage 2.
6) If any player had less than 4 threat in their staging area when stage 2 was discarded, reveal 1 additional card at that stage (per the stage 3A instructions).
The bit about repeating step 4 is not actually written on the stage 2B quest card, but that is an error. You should not leave any cards in stage 2b.