Arrowverse: Every Major Easter Egg, Clue & Reference To 'Crisis On Infinite Earths'

That brings us nicely to this season's crossover which, for lack of a better term, had infinite references to Crisis On Infinite Earths - one of which was revealed before it even aired.

The main "antagonist" of Elseworlds, Mar Novu a.k.a. The Monitor, had a major role to play in the iconic comic, bringing heroes together in order to combat the Anti-Monitor - who was attempting to destroy the multiverse.

While his Arrowverse incarnation was a little more mysterious, the cosmic being did play a similar role in the crossover, giving the Book of Destiny to the unhinged Dr. Deegan, allowing him to rewrite reality in an attempt to test Earth-1 and, as a result, find worthy heroes who could stand up to the impending Crisis.

Much like the character became the foundation for the Crisis in the comics long before the storyline itself, he played a similar role in Elseworlds, forewarning of its eventual arrival and attempting to do something about it.

Given his comic book history, The Monitor's inclusion alone was a big enough reference to the Crisis, but his plan to combat it has made it official - the Crisis is coming and Earth's greatest heroes must be ready.