AC2020: Tag, you're it!
A word on the percentages mentioned below: alone, they do not show that editors are working together. 38% of my edits are also to pages that MrX has edited at least once within an hour. That percentage drops to 10.6% if we drop my talk page, and anything related to Tulsi Gabbard, Bernie Sanders, Jill Stein and disciplinary noticeboards, where we held opposite positions. (much of what remains is related to HRC, RS/N, NPOV/N, BLP/N where we were not tag-teaming either).
O3000 - X
33% of O3000's edits to Wikipedia have been to pages that 03000 & MrX have edited within 1 hour of one another. Some of this is related to Donald Trump. MrX has contributed to the talk page 1582 times and O3000 had done so 886 times. However this is not the only page on which they coordinate efforts. (evidence: see the caveat above, though 03000's talk page does not appear, it is possible that they have disagreed on pages I have not looked into their interactions on. I have never personally seen them take opposing positions, though.) A high percentage can indicate being targeted just as it can indicate working together (whether harmoniously or in an effort to overwhelm dissenting opinion). A good example is the Media coverage of Bernie Sanders entry, where O3000's first contribution was to revert me 9 minutes after MrX filed a 1RR violation complaint due to an oversight on my part. This ensured that I could not undo my contribution and that I would be warned by El C despite not being given this opportunity: 19:29 12 Jan MrX - O3000 19:38 12 Jan (first edit to the page)
Similarly, when the page was brought to AfD for the 3rd time, they both voted delete within 2 minutes of one another:
They have consistently appeared together at drama-boards in an effort to prevent me from editing Wikipedia: AE 1, AN 1, AN 2. O3000 also aided Sagecandor/Cirt at AE in having me blocked from the site in the first place.
Their involvement in the escalation on "the C"'s talk page is also worthy of note. Chronology:
- El C deletes my request that he stop harassing me in a TP section he started with my user-name in the header 
- 03000 shows up 4 minutes later to make a "joke" in the same TP section with my user-name in the header 
- El C encourages this behaviour in the next edit
There can be little doubt that O3000 has worked in concert with Sagecandor ("the" CIRT) (Editor Interaction) & MrX.
Snoo - X
Perhaps I should update the following spreadsheet compiled in February (before deciding just to "let it go"): 
- (unpinged) 02:20 5 Jan Snoo - X 01:58-14:15 5 Jan (pinged): RS/N concerning whether Honolulu Civil Beat was an RS concerning Hawaii representative Tulsi Gabbard
- 00:18 12 Jan 2020 Snoog, 20:28 12 Jan 2020 X (both remove the same paragraph containing two RS, MrX on the grounds that one of the two sources did not contain such a section title (false), which he called "fishy")
- 00:23 12 Jan 2020 Snoog, 20:18 12 Jan 2020 X (removing an article -- attributed in wikitext -- by Bernie Sanders in the Columbia Journalism Review from Media coverage of Bernie Sanders)
Dan the Plumber - X
20% of the edits made by Dan the Plumber (Sayerslle) were to pages that MrX also contributed to on the same day (easy to read spreadsheet made from Editor Interaction Tool results). Dan the Plumber is the same sock that MrX brought someone to AE, then ANI, for reverting. This account caused a user to leave en.wp in February 2019 and was very active on Tulsi Gabbard.
Later manifestations of this sock included The Bone Dorchester and Bulldog Antz (cf. Bishonen telling them they would be unblocked in 10 minutes despite harassment that would have led them to be indeffed if it had been directed at, say, El C rather than at me).
Content Editman - X
Screenshot of spreadsheet compiled 3 months before the former was banned as a sockpuppet:  The spreadsheet shows that 19% of the sockpuppet's edits were to the same page as MrX. More specifically, on Tulsi Gabbard we can see the convergence of their interests:
(look back at the AE case to find them reverting the same things)
WMSR - X
Neutrality - X
sorted 7-day interactions
Sagecandor - X
sorted account lifetime interactions
Symmachus Auxiliarus - X
Of the 1289 contributions Symmachus Auxiliarus has made to en.wp as of 27 June, 333 were made to a page MrX has contributed to (in many cases the same day). (26%, see screenshot of spreadsheet)
They have made at least a dozen edits in two different cases to defend Snooganssnoogans at ANI , and are a member of the 100+ comments to Talk:Donald Trump club (like MrX, Snooganssnoogans, and O3000).
They were the first to propose boomeranging me for a legitimate ANI complaint about Snoog's incivility, copyvio, and source distortion at ANI.
In that case they made the following claim: Snoogans does indeed make sweeping and opinionated statements about things, which probably aren't always kosher for article talk pages, but they rarely say anything directly about an editor, especially a specific editor. The highlighted part is false and had even already been shown to be false in that very thread.