Here is a patch with the ending almost finished. I implemented the black screen decision boxes in Prehistory and 605 thanks to a ChangeLocation in overworld events (instead of codifying exits in every location), but I haven't done this in 1005 yet because the overworld code is slightly different there, for some reason. It shouldn't be too difficult to figure out. I'll update the wiki later, but note that the decision boxes are using location {1EF} slot and mem 7F00F9.
EDIT: By the way, it's 1 a.m. so I'm off to sleep, but I'll reply to Darkken's post in Graphic Hacking tomorrow concerning Kasmir and King Zeal.