In the December PvP update, Niantic returned 12 previously Legacy moves into the normal movepool. While it was absolutely a fantastic start, there are still a bunch of valuable PvP legacies that 99% of players can't access.
But, if Niantic is willing to give us these, they might be willing to give us another wave of legacies in the future, which means more Pokémon you no longer have the leisure of writing off because they can't get their most useful moves!
Rules for inclusion
The move must currently be Legacy (non-TMable) and non-event exclusive (see: Psychic Gengar, Ice Shard Lapras, Blast Burn Charizard)
The move must be learnable in the main series (the first wave of legacy moves came about because Niantic gave Pokémon moves they could not actually learn in the games)
The move must have some potential PvP relevance for that Pokémon (so no Dark Pulse Gengar, because Gengar isn't PvP useful)
The move must be learnable by that Pokémon in the main series. Chansey has Legacy Psybeam, but cannot actually learn it in the main games. This means that they're incredibly unlikely to ever come back, to keep consistency between GO and the main series games.
The move must be good now. Niantic certainly could buff Zen Headbutt to be Psychic-type Razor Leaf, but until they do it's a terrible move and isn't worth adding back to a Pokémon (Sorry, Porygon).
With some niche relevance every time it's been legal, Ominous Wind has always been an interesting alternative to the Shadow Ball variant of Golbat for those who had access to it. Less hard-hitting immediately, for sure, but that 10% chance of going Super Saiyan is tempting.
So powerful Silph had to ban it in Sinister, tacking Ghost coverage onto Hypno makes it an incredibly strong generalist in addition to its strength as a Fighting counter. This was a super notable exclusion from the December PvP update's de-legacying given how useful it is. The other legacy Psyshock variant hasn't been useful yet, but it could certainly happen.
Weird Green Swampert has a history of being overshadowed by other water-types and mudbois, but that doesn't make it bad. It just needs the right restricted metagame to shine, with Mud Shot + Surf and Earthquake being a potentially very powerful setup. Possibly even more importantly, if Earthquake were TMable, you could use it on the absolutely fantastic shiny form.
Available for Not Long Enough, this is easily one of the rarest legacies out there! While your Blaze Kick + Blast Burn one is definitely useful, it's worth trying to find a second one to run Blaze Kick + Stone Edge if it ever returns to us. Blaziken currently lacks real anti-Flying and anti-Fire coverage, so this set could be give Blaziken some real options for its charged moves.
While the current Poison Jab variant is probably better in a vacuum, we don't really exist in a vacuum, and Bug-type fast damage could certainly be more useful in a Psychic-centric metagame. Paired with Fell Stinger, Bug Bite Beedrill could be used to really power out some super effective damage.
Poison Fang moth has been incredibly useful in multiple Silph formats, from Twilight in February to just this month with Timeless Cup, making it another strange exclusion from December's wave. While Venomoth can certainly function with Psychic, Poison Fang's ability to bait out shields (and pressure Fairy-types) makes it more or less the most useful version of the mon.
Kinda weird that Ninetales doesn't have a good Fire-type move, huh. Like with Venomoth, the non-legacy Psyshock+Solar Beam has had some viability in Rainbow and Timeless, but in Ferocious it really needed Flamethrower to stand out. Ember, also Legacy, is strictly worse than Fire Spin and can remain in the trash. If you don't have a Solar Beam one full prepped already, keep an eye on wild Vulpix to see if you can hold onto a good one!
-0.5 DPT weaker and +0.5 EPT faster than Air Slash, the double legacy Wing Attack + Flamethrower has had niche relevance wherever Charizard has gone. However, returning Wing Attack to Zard's movepool could make Wing Attack + Blast Burn possible, giving Flying fast move Charizard some options!
Was it top tier in Ferocious? Eh. Was it usable? Definitely. Did most people get to use it? No. Returning Fury Cutter would give King the speed he needs to stand out from the bulkier Queen, something he can't do when just relying on its current Poison Jab set.
While Skull Bash has come out on top as the most useful move in many formats, that doesn’t make Dragon Pulse any less relevant as a strong anti-Dragon option while keeping it an incredibly solid generalist. Also making Ice Shard and Ice Beam TMable while they’re at it would be nice.
The angry monkey got a nice buff with the change to Night Slash and Close Combat, but if you don’t want the all-in risky option with Close Combat, Cross Chop would be a fantastic choice.
Honestly, in most cases Machamp would rather just stick with Rock Slide, but there do exist cases when Stone Edge's raw power wins out. While this probably does more harm to your TM pool than it does good for the mon, it's definitely a move that could come back.
Shadow Ball Haunter’s historical relevance as a skill-intensive powerhouse makes it another strange exclusion from this release. While Sludge Bomb and Dark Pulse have been viable alternatives through the last year, nothing's really matched up to the raw power of Legacy Shadow Ball.
Poison Jab / Icy Wind / Drill Run
Peck's kinda mediocre, Waterfall doesn't make it stand out, and Water Pulse is bad. However, with its interesting melange of coverage and the recently buffed Icy Wind, Seaking could really stand out in the right metagame. Drill Run isn't necessarily the most exciting move in the world, but it could further improve its versatility.
Don't get me wrong, Victreebel's good, and Leaf Blade's better than Seed Bomb, but Weepinbell's current fast movepool is just so disappointing. Razor Leaf would bring it into usability.
Rock Throw / Rock Slide
With Omastar learning Rock Throw in Let's Go Pikachu/Eevee, this isn't an illegal moveset anymore. Often hunted down for raids, Rock Slide's functionality as a stronger alternative to Ancient Power (without the buff chance) makes the mon much more versatile. Past that, Rock Throw makes Lord Helix work so much better as a Flying counter.
With Alolan Raichu getting it, why not? Thunder Shock sacrifices a little bit of Spark's power for a bit more speed, letting it really power out those Brick Breaks and Wild Charges. In the end it's all but a direct upgrade, which would help Raichu stand out over its (obviously much cooler) floating cousin.
Thunder Shock / Discharge
Another case of Thunder Shock > Spark, Magneton also prefers its second legacy move in Discharge, allowing it to more reliably perform its role as a hyper-spammy Electric-type.
Waterfall's good, but Hydro Cannon's better, and 2.66 EPT isn't enough to fully exploit its power. Picking up slightly higher energy generation with Water Gun would allow Feraligatr to work as a more offensively oriented version of Blastoise. Probably not enough to save the mon from obscurity, it would at least be an interesting pick.
Probably not better than Dragon Breath in most cases, Water Gun's alternative coverage brings with it some interesting matchup spreads (notably against Steel-types). Like with Feraligatr, Waterfall's low energy generation just can't quite cut it, especially with Kingdra's expensive charged moves.
Saving the mediocre-est for last, Legacy Pidgeot was…nearly relevant? Once? For about a week in Jungle Cup. Wing Attack takes this surprisingly tanky bird from "Worse Noctowl" to "Still worse Noctowl, but it's probably usable now at least." Wouldn't be too terrible if this stayed legacy forever, but at least it would be a reason to ever look at the mon.
Huge movepools definitely make getting the right moves really frustrating and costly. Variance means you can spend like 9 charged TMs on a Pokémon with only 3 available moves. However, it's arguably even more frustrating to know there's a move you need that you just straight up can't get without hunting down some random person who forgot to clean out their 2016 collection.
This first set of Legacy returns is a real blessing to those who didn't happen to have these movesets in their collections, especially super-rare ones like Dragon Breath/Dragon Claw Dragonite. But there are many more legacy moves, with much more utility, that are still inaccessible to 99% of the player base. Great start, Niantic, and thank you, but please keep it going.