This disaster of a post seems to be the result of two distinct events that compounded upon each other. Unfortunately the details can be challenging to suss out, so the following is a best effort explanation based on available evidence.
The initial post was published by @roach shortly before 4AM UTC [1]
A great many users received notifications that they had been tagged in it, but found no such tags present [2][3][4]
@roach edited the post several times over the next hour, two remaining version contain a block of usernames, followed by the string “mfc-ads” repeated 1,000 times [5][6]
A screenshot posted by @the-universe-at-large (current URL @bleary-eyed-blue) shows what may be the version of the post they had been tagged in, also containing a block of usernames [7]
Some users replies suggest that they originally reblogged a different version of the post than they are attached to now [8][9]
A possible reconstruction of events involves @roach repeatedly editing the post to add “batches” of user tags, before editing it again to remove them
That very same day, Tumblr began switching from the older “indentation” reblog format to the current “caption” style format [10]
@the-universe-at-large’s reblog (and others [12]) partially retained the “indentation” formatting despite the wider website’s migration [9]
When @high-saffron (now user @anthraxplus) reblogged @bleary-eyed-blue’s post [13], they noticed that @roach’s root post (in the new format) was re-inserted into the beginning of the chain every time there was a reblog, and did several times [13]
As duplicates accumulated in the top of the chain, the post seems to have more fully migrated to the new format some time before @lenasai’s reblog. However, some quirk in the process flattened the whole corrupted chain into a single post, which then had its authorship attributed to @lenasai, as the most recent contributor [14][15]
The @roach conga line continued to grow irregularly for some time, before settling on the 28 currently present
[1] https://www.tumblr.com/dnaha/128161107666/roach-hi-yo
[2] https://www.tumblr.com/lmporterroblnson/128162201579/roach-hi-how-was-i-mentioned-in-this
[3] https://www.tumblr.com/the-a-r-t-i-s-t/128164407735/roach-hows-everyone-doin-tonight-i-just-broke
[4] https://www.tumblr.com/paledrake/128162523614/roach-hi-i-broke-tumblr-they-somehow-tagged
[5] https://www.tumblr.com/chocolatewarkittens/128162793370/roach-hey-tumblr-did-you-know-that-the-text
[6] https://www.tumblr.com/i-taste-melancholy/128162743855/roach-hey-tumblr-did-you-know-that-the-text
[7] https://www.tumblr.com/bleary-eyed-blue/128168632021/roach-hows-everyone-doin-tonight-i-just-broke
[8] https://www.tumblr.com/whistlingwadewilson/128162268296/roach-i-broke-tumblr-lmao-yeah-i-did-know
[9] https://www.tumblr.com/bueno-desolation/128164399483/roach-hi-doing-good-thanks-for-asking-how
[10] https://www.tumblr.com/@support/128127169452/ever-see-a-crazy-long-indecipherable-reblog-chain
[11] https://www.tumblr.com/anthraxplus/128168673257/the-universe-at-large-roach-hows-everyone
[12] https://www.tumblr.com/se7-seethe-blog/128161624861/roach-hi-sorry-have-we-met
[13] https://www.tumblr.com/anthraxplus/128168703042/the-universe-at-large-roach-roach
[14] https://www.tumblr.com/busytown/128222679024/dangergays-the-universe-at-large
[15] https://www.tumblr.com/lenasai/128223024163/roach-hows-everyone-doin-tonight-i-just-broke
