Based on character rosters, this episode likely occurs before the events of Avengers: Ultron Revolution , as Ant-Man is still actively operating with the Avengers in New York.
The chaos begins on Halloween night when a magical surge affects the children of New York City. [S4E20] Strange Little Halloween
The trio must track down the source of the magic—revealed to be the villainous Baron Mordo —who has stolen a powerful artifact from the Sanctum Sanctorum to wreak havoc. Based on character rosters, this episode likely occurs