Thank you so much for responding to everything!
About index -1 errors:
What I noticed is that it's very likely that it happens if it's the first time I'm doing it during my game session and the last game session wasn't shut down because of the error. Which sounds weird, but that's really how it is. If the game shut down because of the error, I can be basically sure that it won't happen again when I start the game once more and use the same circle again right away then. Also if it works, I can be sure that every other grass circle on the same map will work fine as well until I switch screens. If during a gaming session I successfully used grass circles on any map before, the chance of the crash happening during the same session on any other map seems to be very low as well, but it happened before. But generally, the first grass circle during each game session when the game session before has been ended normally and not with a crash by this error is the "dangerous one".
About the game lockup:
I remember Lita saying something along the lines of "Everyone, we need to talk", everyone else stepped closer to her but then Lita never talked. I believe it was the first thing she said when she came down the stairs after her father went to sleep.
About the last dungeon:
The elf was invisible. Absolutely, totally invisible. I know that for sure because I checked literally everything in that room when I discovered that I could get a "all you can see behind the gate is a pile of rubble" (or something like that) message when I checked the cracked gate and I was desperately looking for clues where the elf could be. I wanted to see if I could check out the other gates and blocked places in the room and for the first time went above the pond and literally bumped into the elf who appeared right that second.
I tried uploading my save file, I hope this works, I never needed to upload anything like that before so I had to google a random website to host stuff like that: Link
I think (not sure) I saved on the screen south of the dragon encounter (which is finished and over); that way you can also see how the message about the Point of No Return keeps popping up there for no reason when I try to switch screens.
Also, since you just said something about items disappearing: That happened to me today before, I had totally forgotten to report that as well over my shock of losing my gold key. It must have happened somewhere in the Holy Land, I believe; I found a Magic Elixir in a chest and when I wanted to use an item in battle I suddenly only had that Elixir and all other healing items were gone! I normally really rarely use items, though, so I might have lost them much earlier and only noticed then. At first I didn't even think much about it since I thought it was actually a plot thing (like the fairy teleporting me but leaving my items behind) and only later noticed they were all gone for good. But yeah, I had been swimming in money so much that I didn't even really care.
(EDIT: Unless you lose all stuff except for the healing items when you enter the last dungeon, the item loss actually affected my whole stuff, not just the healing items and/or gold key. I just checked. I usually sell my unneeded equipment, but there had been things I've kept - like the Ring from the Well+3 since I still hadn't decided if I should give it to the NPC or not. My inventory is VERY empty - I check that thing so rarely - I don't even have my crafting stuff anymore except for an Essence I probably got from a boss encounter. Maybe I lost much more than just my gold key, uggh. I suppose it's okay, but still. Maybe that's also the reason for the small bug I mentioned below, about the quest person in hunting range giving me her quest again. Maybe I literally lose the quest since it's stored in my inventory.)
Thank you so much for helping me out so quickly! As for when I downloaded my version, that was Monday the 6th on 3:30am German time (it's 5am on the 9th right now here.).
Also another, super-small bug: Once I've done the quest for the old man wanting to see the elven shrine in the Holy Land and he gave me my reward, he just stands there and doesn't talk to me anymore. Also he was totally gone during the vampire assault and afterwards until I returned from the Holy Land and I had already been scared he wouldn't come back.
Oh, and the person with the bugged hunting quest keeps giving me the quest anew ever so often for a reason. Not that it matters anymore since all my quests have disappeared when I entered the last dungeon (probably intended, even though I can backtrack).
Aaaand another small bug which was weird: After the big cutscene at the beginning of the final dungeon (trying not to write too many spoilers here for people who read this...) when all the NPC allies first come and then retreat, I can go out of the front door of the dungeon for the first time and use the crystal to warp around. But all places are suddenly "stuck", as in the screen doesn't scroll anymore, so I can't move around much. I can still go into doors and all when they are on screen (like in the Bazaar, the upper door to the armory). Things worked again when I progressed a very tiny bit and saw another small cutscene (about Lita sending a certain dwarf back because she wants to handle things alone) and the dungeon began for real. Then the screen scrolling worked everywhere again.
EDIT: More bugs I remembered! There were several sprite errors during the Orlian time. The first time it happened after I had been told in the temple to stay at the Inn for free. When I talked to the Innkeeper, Doren started to talk to her and for some reason, the Innkeeper walked left a step and then faced an empty space while talking. I suspect Doren was supposed to appear when he started talking, but never did. This continued during the next scene when Doren and Seri talked while Lita and Adrian played cards. Durng the whole scene, Seri's sprite was missing. Which was really sad, since it's obviously an important scene. I actually reloaded and watched the scene again because I wanted to see if that fixed matters, but it didn't.
Also after the vampire attack on the temple, when I am supposed to go to the Holy Land and some normal temple NPCs have returned, but the dead NPCs are still around, the nun in the temple basement who was yelling at the man sleeping on the floor is still there, yelling... except that the man sleeping is gone, so she's yelling at no one, lol. After the Holy Land, once the dead bodies disappeared from the temple, the sleeping man was back.