3. The Death Of Captain America
This seems like an inevitability if Captain America: Civil War follows the events of the comic books. After being taken into custody, Steve Rogers is shot outside a courthouse by a sniper rifle wielding Crossbones. There's a convoluted aspect to the whole thing where he's basically also shot by Sharon Carter and time travelling bullets, but just forget that for now! Providing the movie spends some time fleshing out his hatred of Steve Rogers, Crossbones is the ideal candidate to be the one to take out Captain America (especially if he then escapes, something which would be a nice way to lead into a fourth movie). Keeping it simple and having the hero shot in cold blood would also be best. Regular moviegoers would never see it coming, and taking Cap off the board for a while would shake the Marvel Cinematic Universe to its very core. It wouldn't necessarily have to be the end for Chris Evans either as a guilt ridden Tony Stark could use an Infinity Stone to bring him back from the dead during the battle with Thanos in Avengers: Infinity War.