Artifacts in Fire Emblem Sacred Stones menu screen

[elipsitz]

The Fire Emblem Sacred Stones menu has a "fog" pattern (BG2) that is made wavy by writing BG2HOFS each scanline.

However, while the game usually updates it by the end of the previous scanline, it sometimes updates it in cycles 0-16 of the next scanline. Depending on what it sets the new offset to, this can cause some slight artifacts. These aren't present on a 2DS XL (and presumably not on a GBA either). See the black pixels on the left:

It's unclear exactly how mid-scanline writes to BGxHOFS are supposed to work (e.g., with activation times):

Screen.Recording.2024-08-25.at.2.54.21.PM.mp4