How Marvel Foreshadowed Doctor Strange's Arrival In The MCU

2. Artifacts & Magical Objects

The first two Thor movies had two of the biggest Doctor Strange references, first with the Orb Of Agamotto appearing as one of the artifacts in Odin's Vault (along with the Infinity Gauntlet). Ultimately, it proves to be a fake, as the real one is located in Kamar-Taj and used to monitor the protective shield cast around the Earth.

Quite why Odin has a fake (or why he has a fake Infinity Gauntlet for that matter) is unclear, but the Easter Egg was there precisely to tease Strange's existence and nothing more.

The Thor sequel also had a couple of Strange links, with The Crossroads dimension where Strange stranded Hulk in the comics mentioned during Selvig's explanation of the multiverse. And his chalkboard also mentions the Nexus Of All Realities, a cross-dimensional gateway between universes that has been part of Strange comics lore.

On top of that, the Quantum Realm's appearance in Ant-Man foreshadowed Strange's manipulation of dimensions and some of his powers and Agents Of SHIELD and Agent Carter both introduced Darkforce, the dark energy linked closely to Strange and mutants at times in the comics.

In other words, Marvel carefully placed mentions of artifacts and magic well before such mystical elements seemed to be a part of the MCU. They laid the groundwork in subtle ways and then, of course, there was that slightly weird explicit mention of Strange...