The Tracking Board claims director Josh Boone filmed material leading up to the reveal, only for studio Fox to "change their minds" after filming had been completed. The horror-centric X-Men spinoff was recently pushed back for a second time earlier this week, citing a need for "significant reshoots."
2016's X-Men: Days of Future Past sequel X-Men: Apocalypse teased the shady Essex Corporation — hinting at the involvement of Mr. Sinister, a.k.a. Nathanial Essex — in its tag scene.
The New Mutants would have "featured" the Essex Corporation and introduced Hamm as Essex, who in the Marvel Comics was genetically altered by the ancient mutant known as Apocalypse.
The mutant granted the 19th century geneticist superhuman abilities, which he would use to menace the X-Men — particularly lovers Scott Summers and Jean Grey — as one of their most vicious foes.
It's unclear if the New Mutants tag would have acted as set up for a potential New Mutants sequel or, like the Apocalypse tag, signal the future arrival of Sinister to the flagship X-Men sequel down the line.
The scene could have been set up for Gambit, another long-gestating X-verse spinoff set to star Channing Tatum as the Cajun mutant, as rumored plot details revealed the card-throwing thief would have come under the employ of Nathanial Essex.
It's also unknown if the removal of Hamm's scene is tied to the tonal shift at the center of those New Mutants reshoots.
According to The Tracking Board's write up, Fox was initially hesitant to go "full horror" with New Mutants, pushing back against the prevalent horror elements and demanding a PG-13 rating.
With Fox and the filmmakers later landing on the same page, both camps "set out to make a [young adult] movie that felt like a cross between Stephen King and John Hughes."
Tracking Board's sources then say It — September's R-rated horror that went on to become the highest-grossing horror movie of all time — caused Fox to reverse course on New Mutants' identity as a "straight-up horror," allowing the teen movie to dip into scarier territory and align with Boone's original vision.
Hamm wouldn't be the first actor to put in work on a comic book movie only for the part to be scrapped: actress Shailene Woodley was to join Sony's rebooted Spidey franchise in The Amazing Spider-Man 2 as Mary Jane Watson, only for the finalized film to excise her involvement and scrub the film of its planned love triangle.
A sliver of Woodley's appearance can be spotted in the finished product as the waitress who flinches when mechanized villain the Rhino drops a car onto a taxi cab.
Actress Jena Malone met a similar fate in Batman v Superman: Dawn of Justice, where her bit role was dropped from the theatrical cut. Her scene eventually made its way onto the extended version of the film released when Batman v Superman debuted on disc.
The New Mutants now opens August 2, 2019.