I don't know if this is a "known" thing or not, but I haven't seen it mentioned either here or on The Cutting Room Floor page, so here it is.
I was poking around in the English ROM, specifically looking at the "Overworld Data" at $06FD10. Each overworld has a 23 byte entry, the first 8 bytes of which determine which background tile graphics to load. In the final release, the 8th slot is always unused. It's set to $80 for all overworlds, which causes the game to just skip that loading routine. If you set it to a valid number instead it will decompress the tiles to RAM at $7EB800, where they will just sit and do nothing. This reminded me of how animated background tiles are handled for locations, so I figured this might be part of a scrapped background animation feature for overworlds.
I decided to check the Prerelease ROM to see if it was any different. Instead of all being set to $80/unused, in the Prerelease slot 8 is mostly set to either $24 or $25. So I fired up the game and checked what was decompressed to $7EB800 and saw this:
It might not be totally clear what that is, so here it is with the tiles rearranged and a couple of special palettes made:
These are leftover animated background tiles from
the old V-Fes 94 "flat" overworld.
Unfortunately, graphics packs $24 and $25 in the Prerelease appear to be identical, so there weren't any other new old tiles to find. The compressed packets are at $059DD4 and $05A183.
