A great plot idea is a crossover centered around a new super - weapon. Maybe some ancient weapon that was lost in the Arrow - verse is found by Hydra in the Agents of Shield world. So the two teams have to work together to retrieve it before it's used for evil. Another popular one is a character - based plot. For instance, if Thea Queen discovers she has some sort of power that is related to the Inhumans in Agents of Shield. She then goes to them for help and that starts a whole series of events that brings the two groups together. Also, a plot where the two teams are forced to compete for a valuable resource, but then realize they need to work together to keep it from falling into the wrong hands can be really interesting.
One idea could be that some of the Agents of SHIELD team get transported to Starling City where they cross paths with Arrow's team. They could team up to fight a common enemy like a meta - human terrorist group that has access to both high - tech weapons and ancient magic.
One popular trope is the team - up. Characters from Arrow and Agents of Shield joining forces to fight a common enemy. For example, Oliver Queen and Phil Coulson leading their respective teams against a new super - villain.
Well, a really interesting plot might involve the Agents of Shield trying to recruit the TMNT for a special mission. Since the turtles have unique skills and knowledge of the sewers and the underbelly of New York, they could be valuable assets. Or perhaps a Kraang invasion occurs in the Agents of Shield universe, and the Agents have to work with the turtles to stop the alien menace. The turtles could teach the Agents some of their ninja fighting techniques while the Agents share their high - tech weaponry and strategies.
One idea could be that Supergirl's powers are misinterpreted by Shield as a new threat. So they send some of their agents to investigate. The agents then realize she's actually a hero and they team up to fight a common enemy like a powerful alien race that's planning to invade both their worlds.
One idea could be that the Agents of Shield discover a hidden threat that is related to an old Avengers enemy. For example, a Hydra remnant has found a way to re - activate some of the technology left behind by Ultron. The Agents of Shield then have to team up with the Avengers to stop this new threat. They could combine their skills, like the Agents' espionage and the Avengers' super - powers.
One idea could be that the Agents of Shield discover a new group of Inhumans with a unique power that could be a threat or an asset. They have to decide whether to help them control their powers or contain them. Another could be an Inhuman from the Inhumans group joins the Agents of Shield to help fight a common enemy, like a new alien threat. And a third idea is that some technology from Agents of Shield accidentally causes a power surge among the Inhumans, leading to chaos that both groups must work together to resolve.
One idea could be that the Agents of Shield discover a new threat that is related to an old enemy of the Avengers. They have to team up to figure out how to stop it. For example, a hidden Hydra cell has found a way to re - activate an old weapon that was once used against the Avengers.
Perhaps a virus is released that targets enhanced individuals. The Avengers are directly affected, but the Agents of Shield has some research on a similar virus from a previous mission. They team up to find a cure. Along the way, they face off against a group of mercenaries who are trying to use the chaos to steal valuable technology from both the Avengers and Agents of Shield.
Daisy Johnson from Agents of SHIELD and Oliver Queen from Arrow would also be an interesting duo. Daisy has her Inhuman powers and combat skills, while Oliver is an expert archer and martial artist. They could fight side - side in a big battle against a powerful villain.
Well, perhaps there could be a crossover where a villain from The Flash, say Reverse - Flash, teams up with a Hydra agent from Agents of Shield. This alliance would be a huge shock as they combine their powers and knowledge. Reverse - Flash's speed and ability to manipulate time along with Hydra's devious plans could create a very difficult situation for the heroes from both universes to handle.