#5 Matt Riddle

Fans who followed the career of Matt Riddle before he made it to WWE already know full well that The Original Bro legitimately intends on defeating Brock Lesnar in The Beast Incarnate's final match. During his time on the independent scene, Riddle even released a T-shirt of his career goals, with 'Retire Brock' as one of them.
Could Matt Riddle be the one to 'Retire Brock'? Well, only time will tell, but, until then, I think a lot of fans would get great enjoyment by seeing two MMA specialists mix it up in the ring at the Royal Rumble. I think this would also be a big opportunity for WWE to build Riddle up as a future star and someone who could be a legitimate threat to Lesnar.
I think the Royal Rumble would be the perfect opportunity for this. If WWE intends to have any NXT talent make an appearance in it, Riddle is one of few who makes the most sense to be used.