I've tried all the VMU packs I can find, but they're all missing this one and there doesn't seem to be much info on the thing in general.
"A kadomatsu New Years decoration is placed. Available 12/26/98 - 01/07/99 (a bug fix version was added on 12/29)."
There's a download for SA1 that would place Kadomatsu (Japanese New Year decorations) around Station Square. The file for it should be something along the lines of "SONICADV_001" and be around 66 Blocks.
It was only available in Japan for a few weeks, and was given a bug fix on the 29th to fix something that apparently prevented the player progressing through Knuckles' story.
Fuck, the only things that even mention it that aren't from 17 year old Japanese websites is info from the article on the wiki here. (I've since updated it. Not sure what that icon is doing there though, since I've only ever seen that used for some of the Samba GP packs)
The closest I've come to finding it is this old Japanese geocities site with a broken email transfer:
There hasn't been that much else come up about it though, aside from the occasional Japanese posts from years ago mentioning it.
Also, a while back my friend made a page for it on the Lost Media Wiki, which can be found here:
Thought people over there could help, but nothing turned up.
I'd appreciate anything that you guys have on this.