#3 Brock Lesnar vs Batista
These two behemoths wrestled against each other in OVW before coming up to the main roster. Years later, fans clamored for them to collide again after they became megastars.
Although the stars aligned on multiple occasions, WWE never went ahead with the dream battle. In 2005, WWE came very close to signing Brock Lesnar again to a contract, after his failed stint in the NFL. A bunch of SmackDown writers had prepared a full-fledged rivalry plan for the returning Lesnar and WWE's new top star, Batista. Lesnar had a meeting with Raw creative team and Vince McMahon, but SmackDown writers were confident that the blue brand would ultimately bag him.
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Days later, the plans went down the drain when Vince informed a writer that Brock Lesnar wasn't coming back. Apparently, he got a better deal with NJPW and went there, eventually coming back to WWE in 2012.