#4 Interference
Imagine a big time main event is taking place for the WWE Championship, and Conor McGregor just wanders into the ring and unloads on the competitors with a steel chair. It would be so random and so baffling that everyone in attendance would lose their minds because it would feel like a genuine invasion is taking place.
You could have a number of UFC guys just show up at different events and build up the possibility of a legit rivalry, when in reality it would be nothing more than the two companies proving that they can work together in harmony.
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It wouldn't be too much of an issue for him to interrupt such a big match either, because if Jon Stewart can get away with it, then pretty much anyone can.
We conclude with perhaps the most obvious move of them all.