The Avengers vs The Fantastic Four, Part 1 - Avengers: Assemble (S2:E7)

Basic Info
The Avengers vs The Fantastic Four, Part 1 is the seventh episode of the second season of Avengers: Assemble. It is technically the show's second crossover episode, if you include Season One's Drax episode, but it is the first official crossover that takes place in two episodes across two shows. The continuation of this episode is found in this Fantastic Four episode.

Synopsis
The Hulk's condition is getting worse, and soon he will never be able to turn back to Bruce Banner. Without any other options, the Avengers turn to notorious scientist Reed Richards of the Fantastic Four for help. This alliance is short-lived, however, and soon turns into an all-out brawl.

Trivia

 * Episode 7 of every Avengerverse show has been a crossover. S1:E7 of Avengers: Assemble included Drax, a well known Guardians character.
 * This episode was originally supposed to be a crossover with Guardians of the Galaxy and was supposed to be a continuation of the Drax crossover from last season. After Fantastic Four replaced Guardians of the Galaxy, however, the plans for the episode were changed.
 * This episode is continued in S1:E7 of Fantastic Four.