He has pretty much every tool needed to be an absolute menace out wide, and since that's where a lot of the goals come from in the modern game, I think it will be prudent to nurture him in that role. He's already one of the best finishers and strikers of the ball in the league, even after the arrival of Ronaldo, so he's lethal in shooting positions. He's equally good with both feet has a mean cross on him, so he doesn't have to Robben it up and cut inside every time. Add Ronaldo coming to the far post from the left wing into the mix and it'll just be assists for days. Nightmare to defend against. He's also good on the ball and has a great burst of pace, so he can create space for himself one-on-one with defenders.
He's pretty much perfectly built to be a menace on that right wing, but I think he lacks a little bit of height and physicality to be as good as a lone striker. Even though we've signed Sancho it makes sense to develop Mason as a wide forward. Ronaldo, Greenwood, Rashford and Sancho is a hell of a luxury to have in the squad. Add Cavani and (possibly) a fully fit and motivated Martial into the mix and we could field two world class attacks every week.