He'd probably be one of those guys with two Noble Phantasms; one that's his "actual" one to show up in narrative, probably either FOXDIE or a crystallization of his role as Big Boss' legacy, and one weaker but more relevant to direct combat that's gameplay, which would basically be the same as his Final Smash in Brawl.
And the Cardboard Box, which would also be a narrative one but which would somehow end up being plot relevant and save the day if he actually appeared in a narrative.
He'd probably be one of those guys with two Noble Phantasms; one that's his "actual" one to show up in narrative, probably either FOXDIE or a crystallization of his role as Big Boss' legacy, and one weaker but more relevant to direct combat that's gameplay, which would basically be the same as his Final Smash in Brawl.
And the Cardboard Box, which would also be a narrative one but which would somehow end up being plot relevant and save the day if he actually appeared in a narrative.
The Cardboard Box will give him perfect stealth. Any other person, servants included, who see his Cardboard Box showing up and be out of place, they will be compelled to utter "Huh, just a box." and just leave it at that.