9. The Infinity Stones (Several MCU Movies)
While this list could easily include them all individually, the four Infinity Stones that have all appeared in the Marvel Cinematic Universe to date are all obviously indicative of the Avengers: Infinity War movies, as Thanos will be hoping to gather them all by the time those movies come around. The Tesseract first appeared in the post-credits scene of 2011's Thor, the Mind Gem first appeared in 2012's The Avengers (although it wasn't confirmed as being an Infinity Stone until 2015's Avengers: Age of Ultron), the Aether first appeared in 2013's Thor: The Dark World and the Orb first appeared in 2014's Guardians of the Galaxy. Since their introduction, we have seen what you can only imagine is a small fraction of what they've capable of - and they've still proven to be quite potent - but one can only imagine just how powerful they will be combined with each other and two additional Infinity Stones (though don't expect them to be as powerful as the Infinity Gauntlet in the comic books).