Crossovers (Concept)

"Yeah, the crossover. Had to take a rain check."

- Nate Heywood on not participating in the Crisis

Crossovers are a series of event that brought heroes of multiple Earths together and fight against a villainous group.

The Flash and Arrow team-up

 * For more information, see Flash vs. Arrow.

Uprise of Vandal Savage

 * For more information, see Heroes Join Forces.

Dominator invasion

 * For more information, see Dominator Invasion.

The first time all of the heroes are fighting for a collective goal is the Dominator Invasion when Barry Allen created Flashpoint and alerted the Dominators. With an army of Dominators about to invade Earth, Barry sought help from Team Arrow, Legends and Supergirl. They fought alongside each other with the goal to prevent the Dominators from invading Earth.

Earth-X invasion

 * For more information, see Earth-X Invasion.

After they defeated the Dominators, they went separate ways until Barry Allen and Iris West's wedding brought them together. During the ceremony, an army of Nazi crashed in and attacked the heroes in order to get Supergirl's heart. Most heroes later stormed their base of operations on Earth-1 but were defeated and sent to Earth-X. With the rest of the heroes stayed in S.T.A.R. Labs, Dark Arrow attacked them along with the members of Team Arrow who arrived for assistance which resulted in the heroes locked up in the Pipeline. Felicity and Iris hid and Supergirl was brought to S.T.A.R. Labs for a heart surgery. During the surgery, heroes of Earth-1 were rescued by the Freedom Fighters of Earth-X and worked together in order to return to Earth-1. The Legends later received the S.O.S. signal sent by Felicity and rescued the heroes along with Supergirl. With two extra assistance, they temporarily took over S.T.A.R. Labs again and destroy Metallo who acted as a guard. They later boarded the Waverider and prepared the battle to fight the Nazis. After the battle, they again went separate ways.

Elseworlds

 * For more information, see Elseworlds.

In 2018, Oliver Queen woke up as Barry Allen and went to work as The Flash as well as the opposite. Knowing the current situation is bizarre, Oliver went to Star City and found Barry in his outfit. They later went to S.T.A.R. Labs and told Team Flash about their situation. However, they did not believe in them and locked them in the Pipeline. They later realised they should seek help from Kara of Earth-38 and escaped to Earth-38 with the brief assistance from Iris. After they explained to Kara about their situation, they started training and adapting each other's personality. During their chat, Cisco arrived and sought help as Central City was attacked by a robot that was accidentally activated by Oliver during his work in the morning. After they destroyed A.M.A.Z.O. with Superman, they decided to fix this situation. Cisco later vibed a vision of Mar Novu giving John Deegan the Book of Destiny and told the heroes they should go to Gotham City. As they arrived, they were arrested and was bailed out by Kate Kane. They later got her help in finding John Deegan and went to Arkham Asylum. However, when Batwoman, Team Flash and Team Arrow arrived for assistance, John started a riot and escaped. After the battle, Barry Allen of Earth-90 arrived in Star City and helped them battle the Monitor who arrived to help John. The reality was again rewritten by John Deegan as Mar Novu returned the book to him. In the reality they are criminals, which then they sought help from Cisco Ramon who is a mafia boss in the reality. With his help, they went to Earth-38 and asked Superman to defeat John Deegan. During the battle, the original reality was restored. When The Flash and Supergirl found a way to stop Deegan, Superman stopped them and warned them they will die. They ignored his warning and Oliver asked for a bargain from Mar Novu, which he will die in Crisis in order to let Barry and Kara survive in the battle. Mar Novu accepted and Oliver destroyed the Book which stopped Deegan. Later, Oliver was awarded of his coming death in the Crisis and accepted his fate.

Crisis on Infinite Earths

 * For more information, see Crisis on Infinite Earths (Event).