Warning: Contains SPOILERS For Arrow, Season 8, Episode 1, "Starling City."
What is the meaning of the Batman mask in Arrow season 8's premiere episode? This question was raised by a preview clip which revealed the trademark cowl of the Caped Crusader apparently having been used for target practice by a certain Emerald Archer, on the island of Lian Yu.
The anticipation regarding Arrow's final season has been building since the season 7 finale. It was here that Oliver Queen was confronted by the Monitor; the cosmic being with whom Oliver had bargained for the lives of his friends during the Elseworlds event. It was explained that Oliver had agreed to travel the multiverse with the Monitor and assist him in preparing for a coming crisis that threatened to destroy all of reality. It was also revealed that Green Arrow must die in order for uncountable numbers of sentient beings to survive and there was nothing Oliver Queen could do to avoid this fate.
Arrow's season 8 premiere, "Starling City," acted as a tribute to the first season of Arrow. The opening scene was taken directly from the first episode of Arrow, with a shipwrecked Oliver Queen lighting an explosive signal fire to get the attention of a passing boat. The only difference was that as Oliver ran to the beach and the approaching ship, we saw a Batman mask on a stake pierced by an arrow, rather than the mask of Deathstroke which was seen in Arrow's pilot.
Oliver returned to Starling City to find a drastically different world than the one he knew, with a new Hood and Canary trying to save the city from the Dark Archer. It was revealed in short order that this Earth was Earth-2, the Canary was the Laurel Lance once known as Black Siren and the new Hood was Earth-2's version the man Oliver knew as Adrian Chase/Prometheus. This proved an interesting and logical twist, given that Earth-1's Adrian Chase was an evil man inspired to follow in Oliver Queen's footsteps and adopt his methods to avenge his criminal father's death.
While Earth 2's Adrian Chase said little about his background and training over the course of the episode, he did deduce that Oliver was from a parallel Earth rather than the Earth-2 Oliver Queen returned to civilization after 12 years. When asked how he figured it out, Chase quoted a saying that had been told to him by his friend Bruce Wayne: "If you eliminate the impossible, whatever remains, however improbable, must be the truth." While the maxim was originally coined by Sherlock Holmes, it proved true enough and confirmed some kind of relationship between the Batman and Green Arrow of Earth-2.
Coupled with the cowl on Lian Yu, this suggests that Earth-2's Adrian Chase had a student/mentor relationship with Batman similar to the one enjoyed between Oliver Queen and Slade Wilson on Earth-1. This likewise suggests an epic battle between the two former allies, where Adrian Chase was forced to fight a Bruce Wayne driven mad by the Mirakuru Serum. Unfortunately, we are unlikely to learn the details of that battle or the rest of the new Hood's adventures later in Arrow season 8, as he perished with the rest of Earth-2 in the episode's explosive climax.