Mario was a no brainer for me; discussing his talent is as boring as talking about a created video game player. My #2 pick, Gretzky on the other hand is one of the most interesting talents in sports period.
Not Bure/McDavid fast, but still a great quick/shifty skater (great edgework too). His endurance is inhuman and I've heard guys like Glen Sather say he plays even better once you get his face flushed. Greatest passer in league history bar none. Crazy accurate shot. But those all play 2nd fiddle which is crazy.
Then you have his IQ and vision... Neurologists actually ran tests on him and broke down his anticipation/vision/hockey IQ:
Anticipation/Hockey IQ
"Gretzky was renowned for his ability to anticipate his teammates’ and opponents’ movement intentions. He was quoted in Time magazine as saying, ‘People talk about skating, puck handling and shooting, but the whole sport is angles … forgetting the straight direction the puck is going, calculating where it will be diverted, factoring in all the interruptions.’ And when Gretzky took control of the puck, another set of extraordinary cognitive abilities would take over – in particular, his long loop reflexes. Long loop reflexes are movement responses to sensory stimuli that involve complex loops of nerve cells in the brain. Gretzky had the fastest long loop reflex times of anyone examined at the University of British Columbia laboratories in Canada."
Vision
"According to Bill Tatton, Gretzky has one other physical-neurological attribute that undoubtedly contributes to his extraordinary success. Gretzky claims that he never turns his head in order to make a pass. In fact, he never looks at the players on his wings before passing the puck to them. What Gretzky is reporting is a much greater than average ability to perceive motion far from his center of vision, and that this motion is sufficient to trigger his passing skills. Most of us spend our lives moving our eyes in order to keep objects within the center of our visual field where visual acuity and color discrimination are greatest. Perception of motion, however, is maximal outside of this area and these moving images are relayed from the retina to those visual cells that Hubel and Weisel studied. These visual cells and their distribution are under hereditary control, but without the proper stimulation during the appropriate window of opportunity they will never develop to their maximal capability. Gretzky had this physical skill and developed it."
Super unconventional combination of cognitive/physical traits maxed out while also being unnoticeable to the average viewer. Gretzky stands out in the NHL the way humans stand out in the animal kingdom imo.