5. Creepy Robot Santa takes on The Avengers
On paper, a large bearded man invading millions of homes on the same night every year sounds terrifying. We accept it as kids because it's Santa Claus, and also we are dumb gullible post-fetuses, but when adulthood rolls around you realize that the man eating your milk and cookies has a rap sheet of misdemeanors a mile long. So when the Avengers Christmas Party is interrupted by some dude in a red suit with the dead-eyed stare of the Burger King mascot, it sorta freaks everyone out.
It wouldn't be much of a comic if Creepy Santa turned out to be Morph playing a Christmas prank on everyone, so yeah, it's a dastardly Terminator-like robot with a neural disruptor. Santa-bot also has some sort of Naughty/Nice protocols running, but it's hard to tell what the criteria is for deciding who belongs on which list. Iron Man could be on the naughty list for anything from arms dealing to operating an exosuit while under the influence, but what has Captain America ever done to warrant a lump of coal? Dude's more squeaky-clean than a mouse being run over by a street cleaner. It makes a bit more sense when Wolverine reveals the identity of the Kringledopper.
Ultron. As in, the villain of the Avengers movie sequel Age of Ultron. In most cases this reveal would mark the beginning of a months-long event spanning two dozen different comics, but the situation was resolved pretty quickly when the good guys figured out Santron was created by a sad human woman who just wanted Santa Claus to be real. She didn't get her wish, but at the very least I'm sure the Avengers can get James Spader to do her voicemail message or something.