I was originally going to drop a tell-all manifesto here, but I think most of my "secrets" have been figured out by now. As with last time, I'll keep it brief, sticking to basic overviews and maybe a few key insights that may be somewhat unique to me. I'm not giving any teams this time, sorry.

There's not much new to say about Mr. Mime. It has so many extremely valuable traits and so few drawbacks. I'm sure plenty of teams exist that don't strictly need it, but I seldom found myself unhappy that I chose to run it. I like it on basically every team. Positioning Mr. Mime to pressure key threats with strong attacks and Thunder Wave is a key skill in this tier.
I think it's a terrible lead. This is admittedly hyperbolic, because Mr. Mime is so good that it won't drag a team down much by being a lead, but its strengths are very often better elsewhere on a team and several other Pokemon just have more tools that make them stronger leads.
Avoid trading your Mr. Mime for your opponent's, unless you absolutely have to or if you simply don't benefit from its traits anymore. When it comes to tough situations in RBY NU, you need to constantly prioritize and reprioritize what can actually win you the game, not just the Pokemon that's higher on the VR.

Playing with and around Charizard is kind of the essence of RBY NU, at least right now. You need to constantly respect Swords Dance Charizard to play this tier successfully. Revenge killing needs to be done especially mindfully in this tier. Charizard can eat entire teams and reverse seemingly lost games. It's arguably broken, but it is an amusingly consistent comeback mechanic for good players that had bad openings, for whatever reason.
Charizard isn't my favorite lead because I don't love wasting such a strong Pokemon right away. However, it has a really desirable matchup spread and is remarkably customizable for a huge pool of matchups and early game lines. Fire Spin is a thing.

I had Venomoth at #2 for a very long time, but a growing appreciation for Charizard and Poliwrath knocked it down a little. Fast and reliable sleep is the dominant reason to use Venomoth, but its typing actually makes it a surprisingly good emergency check to a lot of Pokemon, as it is actually pretty tricky to hit for super effective damage. Speed and status also make it very difficult to set up on, at least compared to other revenge killers. Also, with a successful Stun Spore on switch or a few Psychic Special drops, Venomoth has pretty good odds to defeat literally every Pokemon in the tier. Humorously, it somehow is one of the better answers to Charizard in the late game.
It's a decent lead with Water-type Pokemon and Magneton cropping up more to answer Charizard.
I don't this Pokemon needs a ban at all.

I wasn't a huge fan of Fearow to start and wasn't even sure if it'd be NU. It's a little strange that it took a minute to click, as I've been a long-time believer of its strengths in even older editions of the tier. But with Electrode and Golem now gone, it's truthfully better than ever. It's obscenely quick and strong and has very few true checks, none of which are particularly strong on their own. Its damage output is just stupid, I really can't stress this enough. I'm not yet content ranking Fearow any higher than this, because it does have solid checks and it can inadvertently empower opposing Moltres and Seadra in certain situations. The exact trajectory is hard to predict, but with more meta development, I can honestly see this bird rise up to #1 in the tier.
It's a decent lead, I suppose.

I might be ranking this too highly. Sturdier teams with smarter pilots have made Seadra a lot less potent. I still like it a lot though as one of the best win conditions in the tier. Success in NU often requires a lot of positioning of your setup Pokemon (usually one or more of Charizard, Fearow, Moltres, and of course Seadra) to close out a weakened team. Seadra is one of the better options to build around here. The choice(s) really comes down to what you want to be able to set up on and what kind of team support you can provide. It was my NU Invitational MVP, for sure (other than that one Venusaur; if you know, you know).
Rest, Hydro Pump, and Hyper Beam are all acceptable third moves. Though honestly, trying to never click this third move is kind of a goal. Maybe Ice Beam has some merit, because it at least has no drawbacks on click.

Blastoise is, on the surface, the least interesting Water-type Pokemon in this tier, having really no status moves of note. But its bulk is perfect for so many random calculations (see Mr. Mime, Charizard, and Fearow, as key examples). It's insane how much mileage you can get from Blastoise's HP if you play it well. It's also surprisingly customizable with a ton of strong moves including Surf, Hydro Pump, Blizzard, Earthquake, Seismic Toss, Counter, Rest, and probably more. I usually used four attacks and was pleased. It is very solid.
While I'm here, I'll say Blastoise is pretty emblematic of another RBY NU tier ethos. You should be constantly keeping calculations in mind during games. I saw a lot of players give up health or sacks for damage that literally did not impact any calculations. Identify your win conditions and set up your opponent's team for that route. Keeping a sack for later is often a lot more useful than the the damage you may get, even when factoring in the immediate free switch. Likewise, knowing when to part with a Pokemon, especially a "good" one, is crucial. Deal and accept damage with intent, and don't give up what doesn't need to be. It seems obvious, but it's not.

Poliwrath is pretty similar to Blastoise. Hypnosis is a good tool, but hardly reliable. I never did, but I can imagine dropping it to make room for more coverage, as Poliwrath has pretty much all the good tools of Blastoise, as well as Psychic. Hypnosis allows Poliwrath to be functional as a lead, but it often makes Poliwrath "feel" worse, given the inaccuracy and lost move slot. On paper, Poliwrath has greater utility than Blastoise, but the slightly lower Speed and additional Fighting-type are major drawbacks. Letting Fearow click Drill Peck and Mr. Mime click Psychic completely freely is just bad.

Moltres has an extremely high damage output and solid bulk, making it at least a pretty good check into a lot of the metagame. In particular, it's quite good at reversing a sweep from Raticate and especially Fearow. I originally had Moltres a lot higher on my VR, but players and their teams are getting better at handling it. Charizard is very good at exploiting it, which is an enormous issue. Moltres is thus just not a very good revenge killer, despite looking like an amazing one. Seadra can be another issue. Moltres also has some consistency issues, as all of its attacks are unreliable for one reason or another. Fire Spin Moltres is held back by consistency especially, but that set is genuinely broken and needs to be banned.
Moltres had a stint in the lead slot, but I think that era is largely over.

Magneton can threaten a huge portion of this tier and even lead pretty well, but low Speed and no coverage make it largely incapable of doing sustained damage comparable to the huge attackers above it on this list. It tends to trade with itself a lot. While targets like Fearow, Charizard, and Water-type Pokemon seem like the main draws to use Magneton, in truth, Magneton is often best at drawing in opposing Mr. Mime and either slowing it down or knocking it out. This opens the gates for one's own Mr. Mime. Thunder Wave is a great tool for support and there is a small handful of games that Magneton is better at securing than any conventional boost sweeper. Did you know Magneton is also stopped cold by Ground-type Pokemon? Because that's an issue too.

With Fearow unleashed, Raticate's lower damage output is pretty noticeable. It tends to be run alongside Fearow, but coverage and the option of Super Fang can create a niche just for itself. Its Body Slam still remains one of the single hardest moves to switch into. Pokemon like Charizard, Moltres, and Seadra can set up on it as they can with Fearow, but with much less safety. Raticate is usually best in the midgame, as it denies entry to sleepers and sweepers. In contrast, Fearow is legitimately good at all stages of the game.

I spammed Arcanine in the lead just to catch lead Mr. Mime and Venomoth. Lead Mr. Mime is pretty bad, so I don't see Arcanine sticking around for much longer, at least at its current prominence. Being good into Mr. Mime is strong, but not totally consistent on switch thanks to Special drops and paralysis. Versus Moltres is similar, looking good on paper, but truthfully being occasionally overwhelming thanks to critical hits. The Speed tier is nice though, helping it to muscle through a lot of tricky Pokemon. It exists largely in the same world as Raticate in regards to stopping Charizard and Seadra sweeps. It's not super easy to fit or justify on a team, especially outside of the lead slot, because it can expose a number of weaknesses to sweepers and has a fair number of competitors.

Golduck isn't great, but I ultimately find myself just being more comfortable running it that using a lot of what's below it. Amnesia is genuinely really solid at sweeping and even reversing sweepers, especially Seadra. Golduck has strong matchups into both Water- and Fire-type heavy teams, really only conceding ground to heavily physically-oriented teams. It does, however, have a lot of competition, and it is not sturdy at all into Swords Dance Charizard. The Speed stat is actually pretty nice though, even when unboosted, getting the jump on Blastoise and Kabutops without having to settle for the bulk of Poliwhirl.

I never really liked Aerodactyl in RBY NU. The Speed tier is excellent, but it's bad at a lot of things that it looks like it'd be good at. It also gets hard walled by a number of Pokemon, though thankfully none of those Pokemon are particularly great. Although, Seadra in particular likes to see this Pokemon on the other side. With Charizard and Fearow being the main win conditions these days though, I think Aerodactyl may be due for a resurgence. While it's not a perfect answer to either of these, if such a thing even exists, it is guaranteed to be able to hit both Pokemon at least twice before going down. With people regularly winning games with Charizard sitting at less than 30% HP, there may be a time for Aerodactyl to come in and stop that. It's very situational and weak, but I think it has its place.

Porygon went extremely underutilized. Teams with limited ability to spread paralysis or land critical hits can lose to a singular Porygon. Thunder Wave is an excellent tool for preventing sweepers from getting going in front of it, as well as for simply securing some value even when faced with an unfavorable team matchup. Porygon is also extremely customizable with a lot of good tools. I think there is a chance that this Pokemon is very underrated, including by myself.

Kabutops is easier to justify nowadays with Fearow being around more. Its Speed and damage output are also good, especially for a Water-type Pokemon. Kabutops just has a very awkward matchup spread that makes building with it a little difficult. A lot of really good Pokemon, as well as some niche stuff, have options for it. It fits well on just a handful of reasonably good builds.

Poliwhirl is incredibly inconsistent, but has a decently high ceiling. I think other Pokemon capture the matchup spread it has with more reliability, but the extra Speed and Hypnosis are compelling. I don't really like using a Pokemon like this in my play, but it is has a place and can be dangerous with good play or luck.

Gastly does pretty well into Raticate, Aerodactyl, and Venusaur, a slew of matchups of dubious value. A decently quick Thunderbolt is a pretty rare trait in this meta, making it good into several key Water-type Pokemon. Hypnosis and Explosion are nice tools as well, especially for supporting sweepers by creating set up opportunities. Being knocked out by Charizard's (and Blastoise's) Earthquake more often than not is pretty dismal though, and most sweepers worth anything can eat through it with limited opposition. I'm extremely torn on putting Gastly in D or E Rank, but thankfully it doesn't matter.

Graveler walls Fearow and Magneton (and Aerodactyl) and has decent damage output. Explosion is also a nice tool (see Gastly). I'd like to see more from Graveler, as it has believers and a few results, but a horrendous Speed and Water weakness make me reluctant to trust it. It may grow better with time though; just look at RBY PU. It's the best Charizard Hyper Beam eater in the tier; just don't miss.

Primeape's peculiar coverage combination of Thunderbolt and Rock Slide is shockingly potent in RBY NU, and a 95 Speed is absolutely nothing to scoff at. Its damage output isn't great, especially when these strong moves are coming without a STAB boost, but it can exploit a handful of otherwise really solid builds and use its Speed to be at least somewhat helpful in most team matchups. Primeape seems very underrated and I hope it at least gets ranked.

Venusaur is tough to use. Razor Leaf is a great option, but without the Psychic or Stun Spore of Venomoth, a lot of Pokemon can give Venusaur a lot of trouble. Certain builds can be very weak to Venusaur though, and it could maybe be used to force out Charizard early or something. I really only considered using it when I wanted Venomoth but felt just a little too weak into Magneton.

Wigglytuff is probably better than I'm giving it credit, but it's really yet to excel. I never felt like I wanted it on any team, and I thought it was bad in the last meta. I hate dealing with the dreadful Speed. Thunder Wave is going to be its defining tool, but I don't know if it's enough, and there are other Pokemon available that offer Paralysis. The Hyper Beam is probably good.

APT can win games. Thunder Wave is pretty good. Next.

I really didn't see, play with, or even think about much of F Rank, so I have little to say.
Nidoking has good coverage and walls Magneton, but loses to a lot of important Pokemon, including some sweepers.
Rapidash can pick off a weakened Charizard or Fearow.
Scyther can pick off a weakened Charizard or Fearow, but with higher accuracy and a worse typing.
Exeggcute has awful everything, but is okay into Mr. Mime and has strong utility options.
Seaking can theoretically do the same things as Seadra, and probably even outclass it in a few rare cases.
Kingler tries its best every day.