Came back to this and decided to mess with the endings a bit because I remembered someone mention talking about exploring during an ending sequence. I did the quest for ending B, threw the wood on the big fire, and talked to it to make the dog show up, and then discovered that most NPCs were still around! I could even go talk to the tree to get more wood, then throw it on the same fire again and replay that sequence in slightly buggy fashion. (Having the power of friendship locked me off from A though.) I tried throwing wood on the small fire and then talking to it, to see if I could confuse the game by doing two endings at once, but that locked me into ending E and most of the NPCs disappeared (including the other fire and the dog) so I couldn't try activating B anymore. For some reason, the shadow guy disappeared when nobody else did, and the throw powerup (edit: also the sapling) stuck around when nobody else did.
BIG EDIT: So if you do what I did, which was activate ending B but then go to ending E at the last minute, you get the normal E sequence, but it turns out that the ending screen displays the B ending message, and the credits play the acoustic or Odin and display the fire picture instead of the special E credits. Since I already had all the endings, I don't know which would unlock, but it's likely that it would unlock the B ending and not the E ending. I think that might be worth fixing! I didn't even have to stone-skip-jump to get to this state, because the rock was still in the river as the doggy song was playing.
Oh yeah, the other thing I noticed was that if you have the cloud raining on screen, and you pause for a while, when you unpause the game a whole lot of accumulated raindrops get dumped at once. That one was pretty funny.