I've been playing PU as much as I can since the Porygon drop though I'm not that good of a player. Nonetheless, I think the current resources are a tad outdated (Fires being extremely good, Rocks being unviable, people are still using Vileplume) so if my dogshit opinions generate discussion that would be good. It's hard to find games so if anyone wants to play PU please ping me on the RBYcord i would like to play more games. I don't have things written about some mons because I don't have anything interesting or new to say about them. Everything under A is unordered.
I feel that Drowzee is the clear #3. Porygon usage means that Drowzee has a consistent setup for Hypnosis, and even though Drowzee doesn't want to click Hypnosis in some games, its traits as a paralysis spreader are still great. It is more threatening than Staryu and Dragonair with Psychic STAB, and the threat of Hypnosis causes the opponent to switch around more than they should. In games with Drowzee on both sides, it really feels that the player who activates their Drowzee first wins, since nothing is comfortable switching into Drowzee. As a lead, I think that Drowzee is quite decent. Fire types are scared of paralysis while Dragonair and Staryu give opportunities to fish for sleep, but if that doesn't pan out, Drowzee can still opt for Twave.
I don't have much new to add about Staryu and Dragonair other than I feel that they are a bit underrated. STAB Surf is very difficult to switch into, and base 85 speed makes it rather easy to use despite its frailty. I appreciate Staryu's offensive presence much more than Porygon's. I'd say that its main strength is that it compresses a lot of roles, being a Seaking check, a decent revenge killer, a paralysis spreader, and a switch-in to more passive mons. Dragonair's typing is useful, as Surf/Thunderbolt Staryu gives Dragonair free entry, and Dragonair can switch into Fire Blasts and threaten paralysis. When I use Seaking, I sometimes run Blizzard specifically to hit Dragonair. Dragonair isn't a defensive liability and is immediately threatening to the opponent, as they have no way of knowing if you are using AgiliWrap. That in addition to Wrap utility makes Dragonair a useful mon. I feel that these traits allow Dragonair to enable some teams that would otherwise be defensively lacking.
Porygon is a mon that I am not that high on in comparison to others. Porygon is a very passive mon, as you are forced to Recover a lot, allowing the opponent to bring in threats. It also is deathly afraid of paralysis, so it has trouble finding entry since everyone is running paralysis spam now. Porygon has the capability to barely wall most of the tier, but the margins are so thin that anything bad happening to Porygon spells doom for it. Lastly, Porygon suffers from terrible 4MSS. I feel that Tbolt/IceBeam exists primarily to allow your Rapidash to progress, but allows the opponent to get a rather free Hypnosis. I like using Dedge/Blizz Porygon to spread paralysis but I feel that this set starts to compete more heavily with other paralysis users, since it is still more passive than other paralysis spreaders. It also gets walled by Omanyte. I also feel that Porygon is often just "tacked on" to some teams. Tbolt/Beam is honestly unnecessary on non-Fire teams. Psychic Porygon is not in a good spot in the meta currently. Machamp usage has dipped a bit and most Gastly users are content to blow up on Porygon. One annoying that I've noticed is that ever since Porygon dropped to the tier, mons like Omanyte no longer click Body Slam to catch a switch, they now click Blizzard to fish for freezes.
In a world where Fearow and Nidoqueen are on every team, and by extension, Fearow and Nidoqueen mirrors are common, one thing I like about Seaking is that the mon doesn't care whether you win the Fearow or Nidoqueen mirrors since those two are probably the best mons for Seaking to set up on. Fearow has around an 18% chance of OHKOing with a crit Hyper Beam, and Nidoqueen has a 10% chance to fish for paralysis. The rise in usage of Fire types also makes Seaking a lot more threatening, since many teams are filled with Seaking-weak mons and rely on one or two mons to not get swept by Seaking. If anything happens to them Seaking just sweeps.
I don't like FBlast/BSlam/HBeam/Agility Arcanine. Instead, I think the Reflect/Rest has more potential. If Nidoqueen is forced to trade early and the opponent isn't running Staryu or Omanyte, Arcanine is extremely hard to dislodge, and the best answer most teams have against Arcanine late-game is to simply fish for crits. Arcanine also has uses outside of a late-game win condition, since its exceptional bulk allows it to switch into other fires and wall them in the mid-game. Its bulk also means it's one of the better switch-ins to Drowzee, Gastly, Pinsir, and in desperate situations, Fearow. Mid-game Arcanine also walls Porygon (unless you get frozen). I'd say that the biggest drawback is that Arcanine has a tendency to be haxed. As a lead, I think Arcanine is okay since although it doesn't really have many "winning" matchups, Arcanine is rather consistent due to its high speed.
I'm not that much of a fan of Rapidash. I still think it's a decent choice but the fact that it is reliant on an 85% accurate move makes it frustrating to use. Non-STAB Body Slam misses out on many kill percentages that it really wants to hit, so I find myself sending out Fearow to revenge kill more often. Dash can revenge kill but is walled Omanyte and the SSJ Arcanine, and on an obvious Fire Blast, the opponent can switch into their own Rapidash or Dragonair to preserve a weakened mon. Rapidash also can't afford to stay in against much, since paralysis might as well KO dash and paralysis spreaders are more common than ever. I feel that Dash also doesn't really add much defensively to a team in comparison to other choices. When building with Rapidash I find myself ending up with a back Staryu very often, as it covers Dash roadblocks (Arcanine and Omanyte) well enough. One thing I do appreciate about Dash is that Rapidash teams are not as worried about winning Fearow and Nidoqueen mirrors, making those mirrors much more favorable. And unlike Seaking, Rapidash is a lot more noncommittal. As a lead, I think Rapidash is just straight-up bad. It's slightly worse than Arcanine in nearly every way, and it also tells the opponent that you will not be using Rapidash late game (it will get paralyzed turn 1). If you click Fire Spin turn one you deserve to be paralyzed.
As a lead, Gastly is inconsistent but decent, but I think that phoopes-style back Gastly has genuine merit. Porygon has to choose between three coverage moves, and Psychic is the least popular of them. When building teams, I like pairing back Gastly with Drowzee to get a very consistent sleep (Dedge is walled by Gastly, Psychic is walled by Drowzee) or with Omanyte (Gastly takes Tbolt well and Omanyte takes Psychic okay). As a lead, I think that Explosion is somewhat underutilized. Even though it doesn't KO Drowzee or Porygon it allows you to bring Nidoqueen for free, and they are forced to sack and probably trade Queens. Personally, I like using lead Gastly with Reflect/Rest Arcanine teams because of this.
I'm very high on Magmar. Back Magmar on double fire compressing Porygon's role as an Omanyte answer while still being a Fire-type probably gives it a niche though I don't think anyone's been trying to build a back Magmar team since Porygon dropped. Lead Magmar is very cool though. Lead Gastly and Drowzee getting more use means that Magmar is more useful than ever in stopping sleep. I like using lead Magmar on offensive teams with a weak defensive backbone that can't really afford to switch around Gastly or Drowzee.
I feel that Omanyte is much better in the meta than I originally thought. Porygon being forced into one coverage move means that Omanyte's crippling flaw of being a Porygon doormat isn't too big of an issue, since pairing it with Gastly or Drowzee means that you can at least get a sleep + Twave/Boom on something, which usually puts you far enough ahead that using Omanyte teams are worth it. I like using Hydro Pump to catch greedier Porygon players but I think Rest has merit, at least for now. Porygon users like saving their mon until Omanyte is KO'd, and in a late game Tbolt-less Porygon beats Omanyte in a 1v1 since they have more chances to fish for freeze. Rest allows Omanyte to have a rather good shot at winning a Porygon late-game. I don't think that Omanyte is as passive as it used to be, since mons like Pinsir have seen a bit of a usage dip, while mons that are more threatened by Omanyte, like Rapidash and Fearow, are more common.
I am also not that much of a fan of Pinsir. Fires/Fearow being everywhere doesn't help, but the rise of paralysis users like Dragonair and Porygon makes life a lot harder for Pinsir since Pinsir likes having a good speed tier. Pinsir doing rather set damage also is a liability, as really silly stuff like a Rapidash or Fearow hard switch become possible. Nidoqueen also no longer being the undisputed number one mon also harms Pinsir a bit, since the ability to switch in is not as important (Queen is still on every team but in some games, Nidoqueen isn't revealed until very late). Pinsir being unable to spread paralysis, its fear of paralysis, and difficulties dealing with Porygon for non-SD sets make it hard to justify over other mons. It still hits like a truck and is one of the better paralysis abusers, and Swords Dance sets are unexplored at the current moment.
I think Machamp suffers from many of the same issues as Pinsir (not a great paralysis spreader and Fire/Fearow). One thing that Machamp has above Pinsir though is that it works rather well on Omanyte teams. Being a good Nidoqueen switch-in and taking rather little from Staryu's and Porygon's Tbolt lends it well for those teams. I feel that Machamp fears Fearow even more than Pinsir though. After switching in on a Nidoqueen, Machamp has to play a guessing game of whether the opponent will switch into Fearow or stay in with Nidoqueen. Pinsir's Slash is more consistent overall.
I am not qualified to talk about Sandslash.
Abra is probably an entire sub-tier below Machamp/Pinsir but it still feels very PU to me. Fearow being on every team is bad news so a late-game Abra cleanup is harder than ever. Rises of fires and paralysis users are also very bad. I still think it has a large amount of good traits but it's constricting to build around Abra. You need a rock so the opponent will not just click Hyper Beam at every Abra impasse and since you are probably using Omanyte, you also need Drowzee/Gastly on the team so Tbolt Porygon doesn't just auto-win against you. I feel that the meta has changed unfavorably to Abra so much that I think its best use nowadays is to use it as a backup Drowzee. (It can revenge something, spread a fast paralysis, and switch into NFEs not clicking Twave).
Graveler very much has suffered from the Porygon drop. I find difficulty in building Graveler teams of old but I think Graveler has some good traits. Nearly every mon has trouble switching into Graveler, barring Porygon, which means that it is a very good Porygon lure. Blowing up on it immediately and then having a bunch of Porygon-weak mons like Seaking is a team structure that I am quite fond of, though it is quite inflexible (Porygon critting or freezing is game-ending). I think that Poliwag stocks will rise soon, since if people stop using Rapidash/Arcanine leads suddenly Poliwag is uncontested with its 60% sleep and can actually do things. On the other hand, I think that Slowpoke will decline since the increased prevalence of lead sleepers and paralysis users will harm its effectiveness. Slowpoke is bulky, but it isn't THAT bulky that it can afford to lose turns to paralysis. Scyther is another mon that I think shows potential but I haven't seen anyone get it to work. It probably has some niche on Omanyte teams.
Weepinbell and Vileplume are probably at the peak of their usefulness in this meta. Staryu is running Surf/Tbolt to catch fire types, which gets walled by Dragonair and the grasses. However, if my opinion that Fire types are not that great catches on, Staryu may sometimes opt for Blizzard over Surf to hit Dragonair, which would cause the grass's niche to evaporate. I think Weepinbell is much easier to build with though, since it is somewhat similar to Twave Dragonair except that it has sleep.
Here are some other mons that may have potential, starting from most likely to least likely.
I find that it is rather easy to force an early Queen trade while using lead Gastly, so perhaps Magneton has a niche somewhere.
Primeape functions very similar to fire leads, except that it does better versus Staryu.
I saw someone using a lead Pikachu and I thought it was pretty cool. It's like a marginally faster Staryu without Recover. 90 base speed paralysis gets the jump on every other sleeper and also speed ties Poliwag, but maybe Abra would be more suited for this.
Pidgeot is the only one of these that I've seriously tried building with, and I can tell you that it's awful. Not learning drill peck means silly stuff like Gastly, Pinsir, and Machamp are suddenly good switch-ins to your Fearow-lite. Being slower also stings and having worse rolls on Porygon makes it not worth using. It's like all the good things of Fearow were stripped away. It could be useful as a lead, though.
Lead Metagame:
Currently, it feels that paralysis spreaders like Dragonair and Staryu are the most common and effective. Fire types generally feel bad to use a lead since they can't guarantee paralysis with Body Slam and their STABs are resisted by these two. Gastly and Drowzee will probably rise in usage since they can get sleep off against NFEs much more consistently than against the Fire leads, though if Magmar were to also rise in usage Drowzee and Gastly would be worse off.