In line with Rocksteady Studios and Warner Bros.' launch of "Batman: Arkham VR," an Easter egg has reportedly been found in an "Arkham Knight" DLC.

According to Reddit, Rocksteady's "Crime Fighter Challenge Pack #6," which was released in January, saw players engage with Wayne Manor. As per the publication, the game allowed player-piano interaction, which further unveiled a wall with notes like "Shrapnel," "He knew his killer?," and "Find the witness."

The mystery of the hidden wall led to more than 400,000 clicks online, Kotaku reports. This is coupled with comments from confused and speculating players trying to figure out its meaning.

As per IGN, the mysterious wall is viewed as a "subtle" outline of "Batman: Arkham VR's" plot, which sees the Dark Knight in search of clues about the death of his friend Nightwing. According to the publication, it is not the first time Rocksteady has teased future "Batman" games in the "Arkham" games.

It may be recalled that in "Arkham Asylum," players can see some references to its sequel "Batman: Arkham City." Conversely, those who played "Arkham City" could find clues at Scarecrow's plot, which potentially serves as references to his operations in "Batman: Arkham Knight."

In this regard, players, just like Batman, may think that the victim knew his killer. As per Kotaku, this leads to events, such as the Dark Knight confronting Penguin about the incident, scrutinizing the bodies in the morgue, and visiting a prison.

Developed by Rocksteady Studios and published by Warner Bros. Interactive Entertainment, "Batman: Arkham Knight" was initially released for Xbox One, PlayStation 4, and Microsoft Windows in 2015. Meanwhile, "Batman: Arkham VR" is set to be released for PlayStation 4 this month.