Yo, time to talk about relevant changes for free interactions. I'm not particularly familiar with the editor on Smogon so sorry in advance for any errors.
Rises:
Personally, I never cared for it, but its niche as a pure Steel type Rocks setter was hard to underestimate, combined with the highest Attack out of all the Rocks setters (tied with Rhydon) and solid coverage let it run a Banded set that tore holes though defensive teams. It was a pretty flexible offensive mon in general. I've seen sets from SubCurse to Life Orb Sheer Force to even Occa Berry. While I can see the meta missing it considering it was A- on the pre-DLC viablity rankings, I feel other mons will fill in the role it had on teams.
LETS GO, I ABSOLUTELY HATED THIS THING. This might be an unpopular opinion, but I feel that Snorlax was constraining teambuilding too much due to its insane bulk (160/65/110, which turns into 160/130/220 against Fire and Ice type moves, both of which are common in the metagame) that gave it a great defensive presence, an Attack stat that lets it hit non-resists hard, the ability to patch up its mediocre defense with Curse and force switches on most defensive mons in the metagame due to its bulk and Curse, which is what allows it to set up in the first place, solid coverage in Body Slam and Darkest Lariat that can slowly wear down checks with Paralysis chance and ignoring defensive buffs respectively, and a typing that gave it only one weakness that has a ton of resists in the meta. That's not even mentioning the cheesy Belly Drum sets that
This would all be fine in a vacuum since Snorlax, by itself, is pretty easily to handle, but the main problem comes with the cores that it can form. VileLax in particular is one of the most annoying cores to face, both of them covering each other's weaknesses extremely well while having reliable recoveries and bulk. Often, when either I used it or I played against someone else using them, it would require an entire team effort in order to take down one of them, and it usually took a very long time to do so, making games boring and unfun to play (this is all my personal opinion btw). Or it would require a not neccasrily viable mon to handle it. Out of every Pokemon on the pre-DLC viablity rankings that's B or higher, the only ones I can see being able to deal with this core are CM Virizion, Specs Drampa, NP Ninetales with Psyshock, (maybe) Raichu-A, NP Toxicroak, a weird Sub Bulk Up Gallade set I've been tinkering with, and Malamar. Adding a bulky Water type to this core limits the mons that can deal with the core even more, and many of these wallbreakers are hard to put onto teams.
Sorry for losing track, I'm just very passionate about Snorlax. As for its impact on the meta, it was an insanely good Fire and Ice type check, and with it gone, I feel like the previously neutered Fire types will be able to rise again.
Not much to say here, anyone who's been playing the tier recently knows how popular it is and how solid of a blanket check it is to many of the tier's offensive treats due to a great defensive typing, an enormous Defense stat, and ability to set Rocks was invauable. Personally I used it on my team after Drampa rose in usage, and with it gone my team is much more susceptible to it defensively. Gonna miss it.
Despite being released midway through the month, it was such a threat in NU that it was able to outpace the second most used mon (Sandaconda) by double. As for its impact, it somehow found its way into Top 10 in usage while it was here, and while I never personally had trouble with it, its coverage + Technician + high Attack and Speed stat gave it insane wallbreaking powers. I can see UU getting bored with it since Scizor was barely able to hang onto OU usage and the most popular mons directly hinder it, but as for when it comes back? I don't know.
Easily the most impactful of the rises, Grassy Surge turned Rillaboom from a solid but underwhelming Choice user into a devastatingly unpredictable mon capable of running many sets while providing great support to its defensive teammates with Grassy Terrian's passive healing. Choice Band, Choice Scarf, Grassy Seed, Leftovers, Life Orb, even Terrian Extender (sometimes) were all viable sets and Rillaboom in general could be modified to fit all but stall teams, which aren't really viable in the meta anyway, and the tier will heavily miss its offensive and support presence. It checked a lot of bulky Waters, so I can see those being on the rise to combat the Fires that are on the rise after Snorlax's departure.
Drops:
Honestly, despite the many drops we got, very few of them will leave an impact of the tier imo. Probably a 1 in 10 ratio, but I'll only be talking about the ones I find impactful.
Both Magic Bounce Screens users from Johto are finally back after a long departure for one and a short departure for the other. Both of them have reasons to be used over the other. Espeon hits harder, is bulkier on the special side, is faster, and isn't weak to Rocks, while Xatu can viably run a physically defensive set, has a 4x resistance to Fighting types moves, is immune to Ground type moves/Sticky Web, has recovery, and can pivot. I can see Xatu being more popular overall but Espeon's niche as a more offensive MB mon is definitively there.
Very good mon imo. Grass Knot to hit Rockers and Gastrodon, dual STABs to hit everything else and bypass Substitute, and enough space for a coverage move or Volt Switch (it also gets U-Turn if you don't feel like dealing with Ground types when gaining momentum). Specs, Life Orb, and Scarf I can all see being viable offensively, and defensively an immunity to Ghost and Water moves is helpful although it's frail otherwise. It also gets Solar Power, meaning it can work on Sun teams despite a lack of boosting moves. Weaknesses to Fighting, Ground, and Fire sorta with Dry Skin sets combined with physical frailty makes it hard to switch into non-resisted moves, but overall I can see it becoming a premier offensive threat.
I honestly have no idea what to think. On paper it looks stupid; solid bulk, insane Attack stat, good coverage, access to coverage and priority to wear down checks, and is the only viable Guts user in the tier, giving it a niche to separate itself from the other Fighting types. But lots of the top tiers in the meta are very good at dealing with it in some way or another, either by stalling it out with recovery or with chip damage with Burn + U-Turn/Volt Switch/Flip Turn. It's also very slow, meaning revenge killers like Passiman and Indeedee-F can take it out with little risk (especially Indeedee, who can set up Psychic Terrian to invalidate priority). Personally I'm leaning more towards a Banded set being viable, trading being able to trade moves and needing a turn to setup with more immediate power and a extra coverage moveslot. Both sets are easily worn down though. I think it's going to hit a weird place in the meta where it's good but generally outclassed.
You know Kingler? NUBL mon that runs Sheer Force Life Orb with setup or a Scarfed set sometimes? Give it a higher speed tier, more coverage, no setup, and effectively what you get it Tauros. With Normal/Fighting/Dark moves that have very little drawback and no recoil (apart from CC), it hits the entire tier for at least netural damage while punishing switch-ins with its sheer power. I may be overrating it a bit, but with Steelix gone and a lack of Normal resists besides Rhydon and Coalossal, I can see this becoming a very good wallbreaker...at least for this month. If/when both Copperjah and Steelix come back, it might see lower usage, but for now little is stopping it from rampaging to my knowledge.
And I think those are the most relevant tier changes imo, with everything else either having a small niche or simply unviable in my eyes. Although I consider myself knowledgable of the tier, I can make mistakes and would love to see possible corrections made to them.