There is an early screenshot from an arcade flyer that shows players fighting two Allens. In the game, there is only one.

In the boss area of the first stage of Metal Slug 2/X, There are three banners with Arabic writing in the background. The first banner reads "Supermarket", but the second and third banners read "I have diarrhea." and "I need medicine." There are several other Arabic signs in the stage.

The game's character select screen notoriously features unflattering portraits of the playable soldiers, which sharply contrasts with the bravado that would otherwise be associated with its militaristic setting. In the years following the game's release, fans speculated that the portraits were intended as either covert anti-war messaging, or as in-universe propaganda disseminated by General Morden's forces.

These theories were eventually debunked in a tweet by lead artist Akio Oyabu in 2025, who explained that the portraits were designed to lend a sense of comedic novelty to the game, humorously standing out from the "handsome men and beautiful women" that were omnipresent in fighting games at the concurrent height of the latter genre's popularity. Oyabu stated that he was influenced by Terry Gilliam's surrealist cutout animations in the 1969 British sketch comedy series Monty Python's Flying Circus.