The midseason finale of "Legends of Tomorrow" teased another crossover could happen in The CW. The finale ended about the Spear of Destiny, something that "Arrow" Season 5 might also address in one of its midseason episodes.
DC's "Legends of Tomorrow" Season 2 ended with Eobard Thawne/Reverse Flash telling his team about the Spear of Destiny. He said the artifact has the capability to alter realities. It can rewrite reality or change history. It is very clear from the finale that the Legion of Doom will be on a quest for the Spear of Destiny when the show returns.
Coincidentally, one of the midseason episodes in "Arrow" Season 5 might also give a nod to this artifact-through the appearance of Spectre. Series creator Marc Guggenheim previously teased that the "Constantine" character might appear in Episode 13, aptly titled "Spectre of the Gun."
According to Moviepilot, the Spectre and the Spear of Destiny go hand-in-hand. The spear is the only weapon that can harm the Spectre, or otherwise called as the Spirit of Vengeance. The first person to manifest as the Spectre was Detective Jim Corrigan. The character coincidentally appeared in the Arrowverse in the series "Constantine."
If Marc Guggenheim's tweet is anything to go by, then "Arrow" Season 5 might bring back Jim Corrigan to the Arrowverse. His presence might lead to the "Arrow" Season 5 and "Legends of Tomorrow" Season 2 crossover.
Jim Corrigan could crossover to the Legends to help the team prevent the Legion of Doom from finding the Spear of Destiny. Likewise, the Legends could also drop by Star City to ask Team Arrow for help about the Legion of Doom. Either of these scenarios could happen, since it is clearly not a coincide, that "Legends of Tomorrow" Season 2 will tackle the Spear of Destiny just when "Arrow" Season 5 will introduce Spectre.