FISHIOUS REND MEGA SHARPEDO
Mawile's merit pre-TRex meta was that it was a TRex counter that can retain momentum with Baton Pass, making it one of the few Trex answers that can fit on offense. Now, that niche is pretty much gone, and looking through the list of the current mons, I'm realizing that Mawile doesn't actually reliably stop a whole lot. As far as responding to offensive threats goes, it counters Sneasel and Absol, which is fine and good, and can fend off Mega Glalie, Aerodactyl, and Scrafty for an amount of time. Aside from that, Mawile loses plenty of 1v1 matchups, and forfeits momentum to a large amount of threats. The problem with defensive Mawile is that it has neither the bulk, offensive presence, or arguably even the longevity to properly do its job, which heavily limits the amount of favorable matchups for Mawile, and is a problem when you consider pretty much every other worthwhile bulky Pokemon in RU has at least two of those qualities. It's hardly even a reliable Stealth Rocker as it has a bad matchup against the two most popular & efficient hazard removers. Flygon can immediately threaten Mawile and outlasts it with Roost, and although Flygon can't switch directly into Mawile very safely, this is remedied by the fact that Mawile gets SR up safely against fewer mons in comparison to the amount of Pokemon Flygon can Defog against. Meanwhile, Blastoise can aim for Scald burns and Refresh Mawile's Toxic, and even with the threat of Super Fang, Blastoise doesn't need to be healthy to 1v1 Mawile. Hell, I am even skeptical of one of its better niches in Baton Pass. Sure, maintaining momentum is one of Mawile's best selling traits as a defensive mon, but when it is so reliant on it (due to its bad matchups against at least ~3 of the opponent's Pokemon in a typical match) to the point where it risks becoming predictable, I start to question its overall effectiveness.
Mawile still has some other sets like SD Pass or even SD Sheer Force (+2 Play Rough does upwards of 68-80% to phys def Alomo, and +2 Iron Head easily OHKOes tank Rhyperior), but those still suffer from huge problems like their awful bulk and Speed, which is only compounded here since these Mawile sets have less incentive / no means to just immediately Baton Pass out. They don't have a lot of safe opportunities to even boost up in the first place.
All in all, Mawile stands to lose to more than it beats, and I feel like these nigh insurmountable issues are just too much for Mawile to remain in B-, and warrants a drop to C+ or possibly even lower than that, as I feel Mawile isn't even as consistent as most of the C+ mons.
Also support Gourgeist-XL's rise to B- (or higher), though I've been using a slightly different set than 49's with Rock Slide > Foul Play, since Rock Slide can catch various switch-ins for decent damage and even fatal in Fletchinder's case. Btw why the hell isn't Ambipom D- too?