ROB's biggest weaknesses are his abusable recovery, lack of landing options, and "combo food" attributes (fall speed, aerial frame data, size). People were kind of shy about abusing these when the game was newer, but now they're being exposed more and more. On top of this, many players need to improve their gyro-stealing game. Don't just hold it and stare at me. Z-drop it! Unless you're Sheik, Sonic, or Bayonetta, you're scaring no one by eliminating your A moves.
In terms of matchups, ROB loses to basically every common/easy-but-effective character.
,
,
, and
all give him trouble, and
and
are pretty awful as well although not as common.
The ZSS matchup is an atrocity. This character's ability to kill off a grab is, in the ROB matchup, only comparable to the Ice Climbers. Unlike the Ice Climbers, however, she has one of the best recoveries in the game and very good grab range. If you're out of upair upair up-b % range, she'll be able to kill you with her many other kill options, such as her strong smash attacks, bair, or down-b. Hell, even if she doesn't get a single grab her up air is still her best tool, invalidating any attempts to land. Raffi-X and Marss fight almost weekly and the amount of times Raffi has won can be counted on your hands. It is 35:65 on a good day.
The Mario matchup is awful as well. Let's give the best juggler in the game a reflector, what could possibly go wrong?
Mewtwo is better than Mario, but still very difficult. His amazing reflector, good juggle game, and mobility coupled with fair basically negate almost everything ROB tries to do. The only real way ROB can win is if the Mewtwo has no clue what to do and hopes shadow ball camping will work out.
A lot of Sonic players don't know how to fight ROB, but the ones that do really expose how bad it can be. ROB is so slow that he can't really beat spindash cancelling into shield, especially if Sonic takes the gyro away from you. Like I said before, Sonic has one of the best steal-the-gyro kits in the game, and projectiles are ROB's only saving grace against it and against spindash in general. Outside of this, Sonic also has a strong juggling game and can harass ROB's recovery with the spring. Some Sonic mains don't use these tools, though, and just try to brute force the MU with aggressive spindash instead of camping like a good boy, and that's a recipe for getting gyro laser'd to death.
Like Mario, Rosalina speaks for herself with a stupid good up air and gravitational pull.
Cloud isn't as bad as he seems on paper -- his size allows ROB to get some decent low-percent combos and he can get shoved around by projectiles if he's not careful, but limit camping, his mobility, and that upair still give us a hard time.
ROB loses plenty of other matchups (
) but those are the worst of it.