I'm going to try to keep this spoiler-free, but there may be limited spoilers for specific actions in the movies.
In Avengers 2, Captain America and Thor work together at least twice, taking advantage of the interactions between Cap's shield and Thor's hammer.
When a group of soldiers (and an APC/Tank) gather to assault them, Thor asks, "Are they lining up?" Cap's reply of "Well, they're excited" is ended with Thor striking Cap's shield, sending a line of lightning at the grouped soldiers.
Obviously, this was Thor using a Line Area attack.
Later, during the climactic fight with Ultron's robots, Thor bats Cap's shield, giving it extra power to destroy several robots.
This seems like it would be built as either a Multi-attack or a selective area attack on Cap's shield.
How, though, would you model the interactions between the characters - it seems like it would be needlessly expensive for each character to have an attack with 'Limited: X must spend an action to enable this' or similar, and it doesn't seem to fit with the flavor the game goes for, either.
How could you have two characters do something like this in M&M 3E?