If not all recruits have been acquired in Chapter 3, there are only 30 Shadowguys and Pippinses dancing (rough split 20S:10P). This is now on their respective wiki pages!
deltarune.wiki/w/Zapper#Tri...
deltarune.wiki/w/Shadowguy#...
deltarune.wiki/w/Pippins#Ch...

The WIP article is here: undertale.wiki/w/10th_Anniv...

Thank you @woedenaz.bsky.social for finding this and @ghilsh.bsky.social for modding and recording the video!

The sprites are already available at The Cutting Room Floor, but there was previously no mention of their use in this scene: tcrf.net/Deltarune/Ch...

There are two other sprites intended for this invisible window, both displaying totally transparent in the same scene. First one has Kris's face illuminated, and the second one shows their eye glowing red. Another invisible sprite is then supposed to show Kris's eye flashing.

deltarune.wiki/w/Kris_Dreem...

Thanks to AGoddessWhoMissesPeople for helping find this!