A few days ago, the Kansas City Royals promoted infield prospect Raul Mondesi from Double-A Northwest Arkansas to the major league roster for the World Series. He hasn't played in the first two contests against the New York Mets, but if he does make an appearance he will be the first player in big league history to make his MLB debut in the World Series.
Even before this Mondesi was a tough prospect to assess. As you likely know, he is the son of former major league outfielder Raul Mondesi and was signed by the Royals as a free agent in 2011. Here is how I rated him pre-season following his 2014 campaign (.211/.256/.354, wRC+ 69 in High-A):
Scouts still love Raul Mondesi: his tools are outstanding, including a strong arm, speed, range, and enough wiry strength to hit for more power as he matures physically. His swing is also well-regarded. And he’s much more reliable on defense than most middle infielders his age. For all that, by any objective metric, Raul Mondesi was a terrible hitter in 2014. His pitch recognition actually seemed to get worse as the season progressed; some sources who got a good look at him quietly wonder if he’ll ever hit enough to play regularly. The big caveat, of course is youth: he was 18 most of the season, extremely young for the Carolina League, and it is no surprise that he was overmatched. Mondesi could still develop into a star, perhaps along Hanley Ramirez lines if the Royals get their wish. Grading a guy like this is tough: excellent tools, weak performance, very young profiles are tough to slot. Grade B.
Mondesi was once again extremely young for his league in 2015, playing regularly at age 19 in Double-A. Once again he did not hit very well, batting .243/.279/.372, wRC+77. Making contact and controlling the strike zone remain significant issues for him, with poor walk and strikeout rates remaining virtually unchanged compared to 2014.
The numbers haven't changed much and neither have the scouting reports. He looks like a player should look: wiry strong, plus speed, plus throwing arm, impressive defensive actions, capable at either shortstop or second base. He can certainly run and he's improved his reads and feel on the bases; indeed, if he sees action in the Series it will likely be as a pinch-runner.
Many Texas League observers were extremely sanguine about his long-term outlook but this was not unanimous. He has a big league future certainly but whether that's as a star, a decent regular, or a bench guy will depend on his hitting and that is still uncertain. The Royals would love Jose Reyes outcome and that is possible, although Reyes as a hitter was well ahead of where Mondesi is at the same stage in their careers. Chris Mitchell at Fangraphs ran some numbers and came up with potential comps like Alex Gonzalez (not bad) and Luis Rivas (not good).
Another comp that comes to my mind is Jonathan Villar, though he's only four years older than Mondesi so we don't know how that will turn out yet.
For me, Mondesi continues to hover in the B+/B range. His upside is enormous and he's been pushed very aggressively, but the risk that he'll never be more than a mediocre hitter seems pretty high to me. That said, even if he's just a mediocre hitter his glove and speed contributions could make him a regular for a decade or longer.
Put another way, if he follows a typical age curve, Mondesi won't be at his peak until the year 2023. Even marginal skill growth during that time will carry him into a long career.