This article explores the way in which the video game that animates the traditional LEGO toys, LEGO Dimensions (Warner Bros Interactive Entertainment / Traveler's Tale / The LEGO Group, 2015) mixes different fictional worlds and franchise brands. I focus particularly on how Doctor Who (BBC, 1936-), the British science fiction series, manages to intervene transmedially in Dimensions itself. I pay attention to the way in which through the combination of different intellectual properties, the transmarca character of LEGO Dimensions seems to appropriate a certain "transgressive dimension of the game" for children (Nørgård and Toft-Nielsen, 2014), although in reality it continues to operate from a logic of shared corporate ownership in which many of the fictional worlds combined are in essence owned by Time Warner (placing the Dimensions in a competitive relationship with the animated toy videogames owned by Disney). Regarding the value that the Doctor Who brand can acquire with its intervention in LEGO Dimesions, I identify it as a particular example of a "What if ...?" Transmedial (Mittell, 2015), arguing that in any case the Doctor Who of LEGO Dimensions fluctuates in terms of the (non) authenticity of your brand. While the Who treatment in the Start Pack is quite true to the format established in the LEGO / Traveler's Tales games, in the Level Pack, sold separately, it integrates more accurately the history of Doctor Who, although here it shows remarkable differences with the television series (Booth, 2015). Although LEGO Dimensions challenges dominant theories about transmedia narrative (Jenkins, 2006; Aldred, 2014), its transmarca character and its potential child / adult audience coincide with those proposed by the approaches established on the transmedia concession (Santo, 2015) and on socialization of the consumer-fan (Kinder, 1991).