Yoshi's companion has only been announced for Mario Kart Tour as it stands.
Following speculation, a new trailer confirms that Poochy, Yoshi's canine-ish companion, will be joining the roster of racers for Mario Kart Tour.
Poochy's appearance is revealed among some other details for the Yoshi Tour update coming to Mario Kart Tour next week. We're not sure whether he'll be crossing over into Mario Kart 8 Deluxe, though.
On the one hand, there are a fair few slots left for DLC characters in Mario Kart 8 Deluxe, but Nintendo has said in the past that the additional racers will be brought in from the series' past, so that may eliminate Poochy from the runnings.