I just took 3rd in this
massive ~130 man Reddit tournament, only playing Diddy Kong. Lost to the same Ness twice due to a few 30% deaths from PKT2. I have some matchup info to share from my experience that I felt was relevant;
Bowser Jr: His car move that goes across the stage destroys bananas and doesn't stop him. SideB and peanuts are your friend.
D3: SideB all the things. Seriously, the kick is OP on his approach if they like to Gordo toss. Generally the same MU otherwise as Brawl.
Little Mac: Shield everything, throw him and everything, gimp with anything. This MU seems horrendous for Mac.
Ganon: Seems to be a repeat of the Brawl MU.
ROB: His SideB is super frustrating and long now, but you can shield the entire thing safely. Just wait for that uppercut animation he does and punish. Bait lasers and top and flip hump when appropriate. Bananas aren't as important in this MU so I say leave them on the ground for space control. Do not try to contest his UpAir, it kills early and has some surprising reach.
Greninja: Fast, but predictable. Watch for the shadow on the ground to catch him when he's teleporting. Monkey hump works wonders because he's so laggy that the Greninja will have a hard time reacting.
Ness: SCREW THIS KID. He should be easy because he's super exploitable, but I'm thinking he excels on Wifi/against slow reactors because of the auto combos he gets if you can't react in time. His throws will carry you far now, sometimes killing even with very good DI and vectoring as early as 90%.