Warning: The following contains SPOILERS for Arrow season 8, episode 7, "Purgatory."
"Purgatory," the final episode of Arrow heading into Crisis on Infinite Earths, borrowed a twist from the comic book miniseries that many Green Arrow fans consider to be his worst storyline ever. What made this particularly perplexing is that there was no real reason for this to occur except to reference a story most Arrow-heads would rather forget.
The action of "Purgatory" took place upon the island of Lian Yu, where Oliver Queen spent most of the "five years in Hell" that transformed him into "something else." It was here that Oliver and company were assembling a weapon under the direction of the Monitor, which would somehow aid them in the coming Crisis. While Oliver had been teleported to Lian Yu by the Monitor, his allies Rene Ramirez (Wild Dog), Dinah Drake (Black Canary) and Roy Harper (Arsenal) had to travel to Lian Yu by airplane to deliver the plutonium needed to power the device.
Unfortunately, the forces working against the Monitor shot down their plane as they were about to land on the island. Roy was discovered trapped under a piece of the plane's landing gear, near a puddle of fuel that was in danger of igniting. Unable to lever the debris off of him, Connor Hawke and John Diggle elected to amputate Roy's right arm since there was no other way to save him. In the comics, Roy Harper lost his arm in The Rise of Arsenal; the final chapter of a storyline that many comic readers consider to be the worst story involving the Green Arrow family of characters ever written. It began in Justice League: Cry for Justice, which saw Oliver Queen join with other heroes to form a more proactive Justice League that would neutralize supervillains before they could become a threat. Their first mission brought them into contention with the supervillain Prometheus, who ultimately destroyed part of Star City, amputated Roy Harper's right arm and killed Roy Harper's daughter, Lian.
Oliver Queen hunted down Prometheus and killed him in the final pages of Cry for Justice. The aftermath of this was explored in two sequel miniseries; The Fall of Green Arrow and The Rise of Arsenal. The Fall of Green Arrow explored how Oliver Queen's life fell apart as Black Canary left him and he was put on trial for the murder of Prometheus. The Rise of Arsenal detailed how Roy Harper returned to heroin use and became a supervillain as a result of the pain he suffered from his injury and his daughter's death. The end result was the completed destruction of Green Arrow's family and the utter ruination of his legacy as a superhero.
What made The Rise of Arsenal particularly vexing for Green Arrow fans was that it came just before the New 52 reboot, which reset DC Comics' reality before any of the stories set up by the new status quo could be resolved. What happened to Roy Harper in the latest episode of Arrow seems equally pointless and arbitrary, except as a reference to the Rise of Arsenal comics. With only three episodes left before Arrow's end and two of those devoted to Crisis on Infinite Earths and a backdoor pilot for Green Arrow and the Canaries, it seems unlikely that Roy Harper's storyline will be resolved.