Hi there! First time poster, long time lurker. I've played through Platinum a few times and I'd also like to contest a couple of the placements here. I'll start with one that I strongly disagree with. Frankly, I don't know what the hell Shinx is doing in A Tier. Every time I use Luxray for a run, I always end up regretting it.
Availability: Shinx comes in on the second route, right after Sandgem Town. Nice.
Typing: Electric. Decent offensively and great defensively. You only really fear Ground types, which are somewhat uncommon.
Abilities: Intimidate is always good, and is recommended over the situational Rivalry.
Stats: A high Atk of 120, decent 95 SpAtk, and a workable 70 Spe (but you will notice it more later on,when your opponents use faster 'mons). With 80/79/79 defenses and Intimidate, Luxray can also take hits fairly well. Sounds alright, so where's the problem?
Movepool: Luxray has the curse of being a physically oriented Electric type before Wild Charge. His best STAB move(s) are Spark and Thunder Fang at 65 BP. Yikes. In theory, 95 SpAtk is good enough for Thunderbolt, but in practice it does about the same damage. While it doesn't hurt to run both for dealing with physical tanks, even non-STAB users like Porygon-Z and Magmortar (we'll get to those two) feel like they make better use of T-bolt. Outside of that you have Crunch and Iron Tail for coverage, which is okay. The last slot can be Thunderbolt, an HM, or HP if you get a good one.
Major Battles
Roark - Can't do much here, but your starter will probably solo it anyway. Although Intimidating Cranidos is definitely helpful.
Gardenia - Luxio's STAB is resisted. Bite can do a little damage, but you can't beat her Roserade.
Fantina - You can rip Duskull and Haunter to pieces with Bite, but beware of the former's Will-O-Wisp. Mismagius is less comfortable. While Bite does hurt, she's faster and at least 2HKOs with Shadow Ball. But if you manage to paralyze her with Spark, you just might win. (That's what happened with me, Luxio was my MVP in that battle.)
Maylene- Intimidate is super helpful here, but watch out for Lucario's Bone Rush. Overall decent as a Luxio, and good if you have a fully evolved Luxray.
Crasher Wake - Avoid Quagmire Quagsire, but otherwise an easy win.
Byron - This is when Luxray begins to fall off, hard. Electric vs Steel sounds good, but let's see here.... Luxray can't touch Magneton, who has Tri Attack to beat you with. Steelix is obviously a no-go, and Luxray can't dent the beefy Bastiodon.
Candice - Sneasel is crippled by Intimidate and slapped by Iron Miss Tail if it lands. Otherwise Piloswine KOs with Earthquake, Obamasnow (I'm sorry) Abomasnow hits back hard (although Intimidate helps), and Froslass has Snow Cloak+ Double Team shennanigans to dodge your coverage moves.
Galactic -Mars and Jupiter are decent matchups, with Zu/Golbat being easy pickings. Saturn's Toxicroak is faster and hits hard with Mud Bomb and STABs. Cryus is a mixed bag. Houndoom is faster and 2HKOs you. Gyarados is an easy win, provided you don't get flinch-haxed. Honchkrow and Crobat are hit super-effectively by y0ur STABS, but they won't be OHKO'd. They are also faster and pack Night Slash or Confuse Ray to mess you up. Weavile is slapped by Iron Tail, but like Houndoom is faster and also flinchy.
Volkner - Can go either way, as expected. You might have the advantage over his Luxray (especially if yours is female) since he has Rivalry. I would stay away from Elective though, as he hit can hit hard with Giga Impact or burn you with Fire Punch.
Aaron - Thunder Fangt/bolt cannot OHKO Yanmega who is faster, has Double Team, and hits hard with Bug Buzz. Vespiquen, like Yanmega, is weak to Electric but is too beefy and can heal or buff her defenses. Pressure is also a pain in the ass. Scizor is possibly winnable with Intimidate, but not without. Heracross is too powerful, and your STABs are too weak. Drapion is too beefy.
Bertha - No.
Flint - Theoretically neutral. But again, Luxray's STABs are too weak while all of his pokemon 2HKO you and are faster (except Flareon, who still burns you to a crisp).
Lucian - Slightly better than Flint since 3 of his members are weak to Crunch, but still unimpressive. Mr.Mime can put up Reflect. Espeon and Alakazam are too powerful. (althought you can revenge kill since they are frail and weak to Crunch). Bronzong is too beefy. Gallade is again potentially winnable with its low defense, but still hits hard and is faster. If Gallade is not Intimidated, he's too powerful.
Cynthia - Spiritomb is annoying, but possibly doable thanks to his low HP. Roserade resists your STABs and 2HKOs you. Milotic is weak to electric, but is quite beefy so in practice it eats your weak hits while firing off Surf. Lucario is faster and hits hard, and Intimidate won't save you from Aura Sphere. Togekiss is winnable. Garchomp is obviously a no-go, but Intimidate is super helpful for your teammates.
All in all, Luxray just ends up being dissappointing in the late game, which as mentioned by others, is quite backloaded in terms of major battles and story. His high attack lets him dominate early- mid game, but he falls off when your oppenents start getting stronger moves while you're stuck with Spark/T-Fang. To me, Luxray feels like C Tier because he's very strong early-mid game, but falls off hard later on due to being slow and lack of a strong STAB, ending up with an overall average performance. I still wouldn't be against using him for a while because as I've said, he really did well up until around Canalave. So I can also see an argument for B Tier. But he absolutely does not belong in the same league as Gallade and Garchomp.
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Second, I also strongly agree with Infernape's argument for moving Porygon up. Contrary to Luxray, Porygon-Z was an absolute beast when I tried it out.
Availability: Mid-game via gift in Veilstone City, and you should have already picked up the Up-grade at the Galactic building in Eterna. You get the Dubious Disc at Glactic HQ, right when Porygon 2 might fall of a tiny bit.
Typing: Normal. Only one weakness to Fighting which is cool. Normal doesn't hit anything super-effectively....usually. But with Porygon, that's not quite the case.
Abilities: Download or Trace, both are situational at best. HOWEVER, if you get Trace, that will turn into Adaptability as a fully evolved Porygon-Z. Adaptability doubles the power of your STAB moves (as opposed to 1.5x), essentialy making them do normal damage if resisted, and super effective against everything else
Stats: Porygon is okay, Porygon 2 is good, and Porygon-Z is just....damn. 85/70/70 defenses, which are good enough. 90 Speed which is okay. And last but not least, a monstorous 135 SpAtk. Combine that with Adaptability, and this thing is just...dirty, man. It's just not fair how much damage it does.
Movepool: Similar to RBY Clefable, Porygon-Z is a pokemon that will eat up a lot of TMs in your run, but it can learn so many that you can build a good moveset without hurting your teammates. However, you will notice the lack of a STAB move until Tri Attack at level 51, or Swift via Snowpoint tutor. Or you can get the powerful, but unreliable Hyper Beam at the Veilstone Dpt. Store. Porygon(2) does just fine without it though. Thunderbolt, Shadow Ball, Ice Beam, Psychic, and Signal Beam are some great coverage options. You also learn Discharge at level 40 and Dark Pulse via TM, if your teammates want Thunderbolt and/or Shadow Ball. And if you want, you can sacrifice a coverage slot for Agility or Nasty Plot, making Cybergoose even more scary. Peace was never an option.
Major Battles:
Maylene - You can hit hard with Psybeam, but you'll likely get KO'd after that. It wouldn't hurt to wait on getting Porygon until after this fight.
Crasher Wake - Gyarados hits hard with Waterfall, but you can hit back harder if you tought Porygon Shock Wave. Quagsire has a low SpDef for you to abuse, and he can't do much back. Floatzle is hit hard by Shock Wave, but he is also decently strong and faster.
Byron - Magneton and Steelix sadly resist your STAB and coverage moves, and you don't have Adaptability yet. Bastiodon isalso quite beefy.
Candice - Sneasel and Abomasnow are weak to Signal Beam, but watch out for Abomasnow's Focus Miss Blast. Piloswine is somewhat even, you're faster but watch out for EQ and Avalanche. Squishy Froslass is hit hard by Shadow Ball, but Snow Cloak + Double Team is annoying as always.
Galactic - Golbat are death fodder to Psybeam/Psychic/Thunderbolt, and Bronzor takes heavy damage while not doing much back. Purugly and Skuntank are somewhat even, but beware of Night Slash flinches. If you can take a hit from Toxicroak, you OHKO it with Psybeam/chic. Once you get through Galactic HQ, you can finally get the monster that is Porygon-Z. If you teach this thing Hyper Beam it will vaporize all targets, but remember that you can't move for a turn.
Galactic 2 - As Porygon-Z you are nigh unstoppable. Golbats KO'd by Electric/Psychic coverage. Bronzor are too weak while zap them to death. If you have Hyper Beam the rodents get vaporized. Swift will do the same, only it'll take a little longer. Cyrus will also get wrecked. Gyarados gets fried by T-bolt/Discharge before it can do anything. everything else gets vaporized by Hyper Beam, though keep in mind that Crobat, Weavile, and possibly Houndoom are faster. Without HB you should still be fine. Fry the fliers. Weavile is hit hard by Signal Beam, but still potentially dangerous.
Volkner - Jolteon is stuck with the weak Charge Beam. Raichu has Focus Blast so be careful. Luxray is too weak to be a threat (Porygon family is genderless, so Rivalry is irrelevant) while you fire off Swift/Hyper Beam or Tri Attack , which possible now. Electivire can hit hard and is faster, so watch out. Although Hyper Beam is probably an OHKO.
Aaron - By now you should have Tri Attack, so you can replace Hyper Beam if you want something more reliable. Or you can simply run both with 2 coverage moves.Yanmega and Vespiquen get fried by electricity. Scizor gets 2HKO'd, and he doesn't have Technician or Bullet Punch. Heracross is tempting with Psychic, but I wouldn't risk it. You hit Drapion on his weak special side, and his attack isn't high enough to ber very threatening.
Bertha - Whiscash is somewhat beefy, but he's no threat. Gliscor and Golem have low special defense. Moto Moto Hippowdon is slow and hit hard by Ice coverage or STAdaptability. Rhyperior is on the iffy side thanks to that nasty Rock Wrecker. I wouldn't try it if Sandstorm is up.
Flint - Your speed EVs might give you an advantage over Houndoom, who is otherwise tied with you. Flareon is slow but can hit hard with Giga Impact, but it shouldn't outright KO you, and now you have a free turn. Rapidash gets vaporized, but watch out for Sunny Day +Flare Blitz. He's also faster than you. Magmortar hits hard, but you hit harder and faster. Stay away from Infernape.
Lucian - If you have Shadow Ball/ Dark Pulse, this is somewhat favorable, but less so if Mr.Mime puts up Light Screen so kill him fast. Espeon is somewhat even, but he's faster than you. You can dent Alakazam, but you lose if Focus Blast lands. Bronzong can annoy you with Calm Mind, but it will only delay you. Gallade is winnable if you have Shadow Ball, since he doesn't have Close Combat. But Drain Punch still hurts. Again though, STAdaptability Hyper Beam vaporizes just about everything, dealing even more damage than Shadow Ball.
Cynthia - Your normal STAB is useless against Spiritomb. Coverage moves should be enough, but you might wanna save Porygon-Z for later. You speed tie with Roserade, and win with Ice Beam/Psychic or Hyper Beam. Milotic is 2HKO'd by Thunderbolt, but watch out for Mirror Coat. Togekiss hits hard with Aura Sphere, but you again hit harder and faster. Stay away from Lucario. And last but not least, the mighty 'Chomp gets OHKO'd by Ice Beam or possibly Hyper Beam depending on your level. Otherwise though, she will do her usual Garchomp things.
And so, I hereby nominate Porygon-Z for A Tier. While it does take a bit of work and resources, the cyber goose will more than make up for it. Even if you forget to check the ability and get stuck with Download, Porygon-Z hits incredibly hard, takes hits okay, and is surpsingly fast to boot. If you do get Adaptability, very few pokemon can seriously threaten you. However, it does take some time and effort to get this monstrosity. Porygon-Z also suffers a bit from 4 moveslot syndrome, as some matchups can be better or worse depending on your choices. For these reasons, I can also see an argument for B Tier. But it is defintely much better than anything in C Tier.
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Finally, placing Magmortar and Glaceon in C and E seems a bit underselling. I've used Magmortar before and I had fun with it. He felt simalar to Houndoom, being slightly slower but noticably more powerful. And while Glaceon comes late and will likely require a bit of grinding (though it doesn't seem too bad thanks to vs seeker), that 130 SpAtk with good STAB and defenses is quite tempting. I highly doubt Glaceon will get any higher than D, but it certainly looks better than the likes of Chimecho and Pachurisu, who are also in E. I happen to be playing Platinum right now (I'm at Fuego Ironworks), and I have a Modest Eevee from Hearthome in the PC. So I'll test these two out and report back!
Or I'll get busy with work and classes (although they are both from home right now thanks to You-Know-What) and forget about this thread. Either way, thanks for reading and stay safe out there!