http://m.mlb.com/news/article/155656276/royals-raul-mondesi-on-world-series-roster
In order to make room for Mondesi on the 40-man roster, the Royals designated right-hander Joba Chamberlain for assignment.
http://espn.go.com/mlb/playoffs2015/story/_/id/13984254/2015-world-series-kansas-city-royals-add-raul-mondesi-roster
By making a World Series roster, Mondesi achieves a distinction never enjoyed by his father. Raul Mondesi spent 13 seasons in the majors with the Dodgers, Toronto Blue Jays, New York Yankees and four other clubs. He appeared in 1,525 regular-season games, made 6,369 regular-season plate appearances and tacked on 38 postseason plate appearances in 10 playoff games -- but he was never part of a World Series roster.