WMG / Tankmen

Tankman is an infectious curse, similar to the Corruption from Friday Night Funkin'

Whenever a Tankman lifts off their helmet in the series they are revealed to be mostly or entirely faceless, even despite having a defined face before recruitment (in the case of Bill, mainly).
JohnnyUtah has stated that all Tankmen are "asexual weirdos". If Tankman really is a form of Corruption, its method of reproduction would be best described as "asexual" and "weird".
As for the reason there are two or more variants of this stuff (Arrowguys, Thugmen, etc) going around, perhaps they were made when the tankmen recruited someone who resisted or blocked some part of the process, giving them more free will and creating a new variant in their design.

• I don't think the Arrowguys are actually infected for the most part. I think that's actually the reason they're so intent on killing the Tankmen, to stop the infection before it can infect all of humanity, and the reason that their equipment looks the same is that they were formerly part of the same organization and/or they raided the Tankman base in order to obtain their armor and weapons.

The Tankmen are humans mutated by radiation

We already know that some great science-related cataclysm happened that left the place the Tankmen reside in as a lifeless wasteland, this event may have been caused by nuclear weapons going off. It may explain why they seem to be stronger than an average human (For example, Skittles managed to break 2 wood pillars in half with relative ease, despite supposedly being shit at combat), or why their skin color is so pale.

The Lennon Noah ARG (and, by way of symbolism, Bob's Onslaught) is really about Tankmen.

Basically, what's going on here is a whole bunch of red herrings towards literally every fnf mod ever while it's all really pointing straight to Tankmen - more specifically, the cancelled Tankmen 0. Lennon is one of the scientists that drove the world to apocalypse, and the reason Tankmen are "Tankmen" at all.

All the father issues in the ARG tie back to the father issues in Tankmen, primarily Skittles shooting a Tankified Bill in the face.The goo that keeps getting mentioned is actually the darkness that Tankmen are encased in, as seen in this image by JohnnyUtah, as well as for a split second in Tankmen 0.5 before a newly converted Bill puts his helmet on.

The AI's connection to the goo is probably an attempt to bring the first Tankman super-soldier to life without a human host, but that just ended up as a monochrome blob (similar to but canonically not the same as the mod's Bob), so Lennon offered himself to become part of the Tankman forces... and his wife and daughter too.

Overall, it seems like the entire Bob mod is nothing more than another cryptic clue in the ARG all about the mascot of Newgrounds itself... which is also why it's a mod for Friday Night Funkin' in the first place.

BUT HEY! THAT'S JUST A THEORY! A GAAAAAME THEORY!