Tbh Cob leaving doesnt affect jelli. We will see other mons rise and Jelli will remain a solid stallbreaker / pivot. I also think its too early to have it drop lol. A mon I think will def rise will be m camerupt mentioned earlier, This thing gives stall balance even ho a lot of trouble. speed creep has begun to gain more usage where checks get 2ohkod lol. Emboar will gain more usage as mlix will still be p good I just cant see jelli dropping imo.
It may be too early for this, but I feel that:
Trevenant -> C+ | There is nothing that really stands out from Trevenant, bar its Attack stat, although it's held back by its Speed. With the Ghost-typing I guess it could be a Spinblocker, although on the Defensive side, there isn't much reason to be used over Gourgeist-XL, bar Harvest. Trevenant can also pull off some sets such Choice Band and Choice Scarf with Trick, although it mostly wants to stick with sets relating to Harvest such as Will-O-Wisp + 3 Attacks. Trevenant shouldn't even start close to B+ rank as suggested by BrandonBeast as Gourgeist can do most everything better defensively, and Exeggutor can do Sub Seed better with Harvest and Sleep Powder, really only leaving Trevenant to sub-optimal offensive sets, which are walled by Pokemon such as Drapion.
it's a little early tbh for people to be suggesting a drop, but I do think that Jelli's S-rank was solely earned on the threat of walling Cobalion while also being one of the single best balance partners for Coba, because no one wanted to click Knock Off and give Coba a +1.
Harvest Lum can also be useful on Trev alongside Rest on bulkier sets to avoid having to switch out, and Harvest Colbur gives it a better match up against Hitmonlee (though you should just be using Gourgeist at that point.) I agree that Harvest is worse than Natural Cure most of the time, but it's not useless.
Steelix isn't easy to slap on offense though, and has no recovery whatsoever while Cobalion was easy to put on any offense team, has good speed and offensive prowess, and the bulk to switch into Glalie easily, along with passive recovery and the ability to sweep. Steelix really lacks all of those things.
A ---> A+
With Cobalion gone, Durant is back to where it was before as a wallbreaker. It sits in a great speed tier, has multiple sets that work, and hits hard, even on resists. While it still has problems that it had before, like being easily beaten by Emboar, and Hustle missing at the worst possible times, Coba leaving makes Durant's job easier.
A+ ---> S
A more controversial nomination but I think Tyrantrum deserves S. It hits extremely hard even without CB, while it can patch up its average speed with Scarf. Has a good matchup against a lot of the meta, especially with Cobalion no longer being able to come in on a choiced STAB move and set up SD freely, so it can work as a revenge killer. It has enough bulk to take hits as well. Tyrantrum is amazing in the current meta, and on the level of the other S ranks, at least in my opinion.
What the hell can tyrantrum do to a bronzong?! If it's not strong jaw than fire fang/crunch are both pretty weak considering the fact that it doesn't get STAB on either of these.
So honestly I've been thinking about what you said about choice banned Trevenant with natural cure as it's ability & this is the best I could think of:
Oh my bad. When I pulled up a set for it on the showdown calc, it showed ice beam. I'll fix my post though, & thanks for letting me know.
