Robert smokes him IMO. Too experienced, good everywhere, with proven defensive grappling. Quicker on the feet with plenty of knockout power and a solid arsenal of standup tools. I keep counting him out because of all the wars he's been in and all the damage he's taken in a relatively small amount of time and he keeps coming back and proving my sorry ass wrong. Maybe in a few years, but as it stands? Nah. I think Rob bloodies him badly en route to a comfortable sprawl-n-brawl UD, maybe even gives him his first (T)KO loss (I doubt it, though -- Robert has been more conservative lately and Vettori has proven to have a helluva chin).
Paulo is an interesting one. Clash of two unstoppable forces IMO. Both are big, powerful guys who like to relentlessly pressure their opponents and fight in the pocket. Both can take a punch and until Paulo's loss to Izzy, neither had been finished. This would be a pure contest of wills. The first round would be absolute fireworks assuming we see a return of the old Borrachinha. I don't know think Marvin could win a pure kickboxing match with him, but I could potentially see him giving Costa fits by disrupting his forward momentum with periodic reactive shots and forced clinches -- wearing on him in both. Paulo has decent TDD and none of his opponents have been able to do much with any of the takedowns they've scored on him, but the sample size has been quite small. He's supposedly a legit Black Belt on the mats. Vettori -- if he chooses to go that route -- would definitely be his toughest test to date. I think it would be worth exploring that option rather than standing and banging with Paulo, at least in the early rounds. Overall... I might give the slighest of edges to Vettori to win by Decision or possibly late TKO/sub, so long as he can weather the early storm (easier said than done). His cardio seems to hold up a bit better in long bouts.
I could see him potentially winning against Cannonier with that relentless pace of his. That's hard to say though, Jared's TDD at MW has actually been decent and he's good at applying pressure of his own to draw out out panic shots before punishing his opponent on the feet (like he did against Jack and David Branch). Both are monstrously big and strong for the division, but Jared has the edge in reach. It would probably turn into a battle of wills. If Cannonier doesn't land a big shot early, I could see Marvin dragging him into deep waters and winning the fight on points or a late finish.
Jack we just saw, though I don't think he fought his best fight. I would have liked to see more exchanges in the grappling department as that was the most interesting question leading up to the fight. That, and Jack would have been better-served to utilize more kicks later in the fight (though his injured leg may have had something to do with him slacking off on that) and straight punches. Regardless, solid win for Marvin.
Yoel is irrelevant at this point. Were he still around, however, I feel like Marvin would be able to win via volume to secure a Decision so long as he didn't get reckless.
Darren's low output, hesitance to uncork that killer left hand of his, and inconsistent defensive grappling could potentially be his enemy here. I could see Marvin getting ahead on the scorecards early and forcing Darren to fight from behind. Till would absolutely land plenty of shots of his own -- solid ones, even -- but not at the clip he needs to IMO. If he could string certain money shots together like those crashing elbows, step-in knees, and of course that left check hook to catch Marvin coming in, then he could really run away with it and win a Decision of his own. But I sort of feel that it's more likely Vettori would steal the scorecards with his pace and willingness to be first in exchanges with a much higher volume (interspersed with occasional TD attempts/clinch exchanges) and -- as cliche as this is -- "killer instinct". This would be a close one.
Entirely possible that I'm just speaking from recency bias and that these top guys slap him down the moment he steps up. I'm eager to watch either way.