I realize some of these are the same tag wandering into multiple places, but I decided to be complete.

The following have wandered into Marvel (Comics)
Natasha Romanoff (MCU)
Peter Parker (MCU)
Steve Rogers (MCU)

The following have wandered into The Avengers (Marvel Movies)
Natasha Romanoff (MCU)
Steve Rogers (MCU)
Thor (MCU)

Wandered into Captain America Movies
Natasha Romanoff (MCU)
Steve Rogers (MCU)

Wandered into Descendants (Disney Movies)
Aurora (Sleeping Beauty 1959)

Into Iron Man (Movies)
Natasha Romanoff (MCU)

Into Maleficent (Disney Movies)
Aurora (Sleeping Beauty 1959)

Into Marvel Cinematic Universe
Rocket (Guardians of the Galaxy)
Valkyrie (Thor Movies)

Into Star Wars - All Media Types
Ren (Star Wars: The Rise of Kylo Ren)

Into Thor (Movies)
Thor (MCU)