system
Given the following post, respond as if you're commenting on Reddit:
human
[MCU/DCEU/FOX] As it stands right now, what is the most conceivable way for a crossover to happen between the Marvel Cinematic Universe, the DC Extended Universe (+ TV Shows), and the Fox Marvel Universe?

Assuming the studios decided to do a huge crossover, who would be the most 'realistic' catalyst to make it happen?

The TV Flashes? Doctor Strange? The Flash in the Justice League? Or a Mutant from Fox? Could someone from the MCU with an Infinity Stone do it?
gpt
The easiest would be the tv Flashes, as they have already been established as being able to breach the dimensional barrier between parallel universes (eg, when going to Supergirl's universe).

Of course, select mutants or Doctor Strange or the right Infinity Stone could also probably do it, but the Flashes are easiest because they definitely have already done it before. If a catalyst for conflict is needed, then there's even 'evil' speedsters that could be the ones to breach into the other universes as well.