Bolded the most important ones. Attacks just ordered by BP, and supports by name. I'm not really covering the important stuff of DPPt or BW because the list could be excesive huge (too much Power Creep), but I'll maybe gonna do that other day. Most of the stuff is mostly filling (as we're just talking about the moves, and not exactly of those users), so, if that's a problem, just focus on the bolded ones.
Also, just covering the moves that were good and created on that generation, usually, the good moves of a generation were also good later (but some were outclassed, like Cross Chop), and some moves not-so-good on a generation could have been good later, like Substitute, but I'm not covering that (like Protect, it wasn't good for nothing at all on GSC).
* = A minor glitch/old mech helped.
** = A minor/mild glitch and/or old mech made it important
*** = An important glitch made it important
RBY (Attacks)
- Explosion* = Free KO when you're almost over? Nice. Breaking Substitute for free? Better.
- Hyper Beam** = 150 BP and no need to recharge when you land a KO or did broke a Substiute? OP.
- Slash** = 99,6% of Critical Hit made it an almost flawless 140BP attack, fantastic.
- Blizzard** = 90 of Accuracy with a great offensive type and power, incredible.
- Hydro Pump = Water were always an important type, and this is one of their important moves.
- Earthquake = Great power, almost flawless accuracy, great offensive type, incredible.
- Ice Beam = Mostly used to "aim for the frezee", and freeze was flawless on RBY.
- Thunderbolt = Nice power, almost flawless accuracy, great offensive type, 10% paralyze, nice.
- Surf = Water were always an important type, and its their best offensive move.
- Psychic = Psychics were powerful on RBY, and its their best offensive move.
- Crabhammer** = Maybe the best offensive move ever created, making something like Kingler usable.
- Body Slam = 30% Paralyze were always great, and 85BP is good enough.
- Drill Peck = Flying were always a good offensive type, and it's a decent move for them.
- Rock Slide = Rock is a fantastic offensive type, and its their best move.
- Swift = On the past, Evasion Clause din't existed, and this was a significant counter.
- Razor Leaf = 99,6% of Critical Hit made it an almost flawless 110BP attack, good.
- Mega Drain = The second best STAB of Exeggutor, decent enough, anyway.
- Clamp*** = Wrap-mechs were too bugged that this was a good move for Closyter.
- Fire Spin*** = Wrap-mechs were too bugged that this was a good move for Fire-types.
- Wrap*** = Wrap-mechs were too bugged that this was an almost flawless 415BP+ attack.
- Super Fang = This move is awesome, too bad Raticate is not that good, but still, nice.
- Seismic Toss = Flawless 100 damage, good for defensive things.
Just ordered by BP. The most significant of them as the move alone? Crabhammer, a highly accurate non-recharging move with 180BP most of the time with a nice offensive type, that's the best offensive move ever created, the problem? Just available to Kingler, who is decent, but its special attack is awful. And most significant by context and general impact? Body Slam, Hyper Beam, Blizzard, Earthquake, Surf, and Psychic, on non-particular order, maybe Psychic if I have to say one.
RBY (Status)
- Acid Armor = 2+ Defense was good, and this was used on old times a lot.
- Agility* = 2+ Speed were always good, but bypassing the speed drop of Paralyze is awesome.
- Amnesia** = 2+ of BOTH Specials is OP, maybe the strongest move ever made.
- Barrier = 2+ Defense is nice, and some important Pokémon are stiil using this.
- Confuse Ray = Confusion was a good status, generally, an important move to annoyers.
- Counter = More used on those times, but, still, an important gamebreaking move.
- Double Team = When Evasion Clause din't existed, this was used a lot with good results.
- Focus Energy** = On Stadium this was great, making you a machine of Criticals.
- Hypnosis = Sleep were always a powerful status, but, here, is OP, and 60% is not that bad.
- Light Screen = Not that good as after, but still a good move and important.
- Lovely Kiss = Better than Hypnosis, 75% is actually good.
- Mimic* = Some Pokémon din't had too much options... and this could be gamebreaking.
- Minimize = When Evasion Clause din't existed, this was used a lot with broken results.
- Recover = One of best non-attacking moves of the game, recovering the 1/2 of your HP? Awesome.
- Reflect = Not that good as after, but still a good move and important.
- Rest = More important on the past along with Evasion, but still an important move today.
- Sleep Powder= Better than Hypnosis, 75% is actually good.
- Softboiled = Chansey is OP just because this, seriously.
- Spore = Maybe the best non-attacking move of the game, but, just Parasect had it...
- Substitute** = More important on Stadium were it actually works better.
- Sword Dance = 2+ Attack were always great, and this generation is not exception.
- Thunder Wave = Paralyze were always a great status, and it's the best inducer.
Just ordered by name. I think the most important move was Amnesia, just nothing reach to the power that Amnesia had, followed by Softboiled and Recover, making those users a lot more important of that they could be without those moves.
GSC (Attacks)
- Megahorn = Heracross was good because this.
- Aeroblast = Lugia was even more uber thanks to this.
- Cross Chop = Figthers like Machamp were viable thanks to this.
- DynamicPunch = Desesperate effort/coverage of some that were always used a lot.
- Sacred Fire = Ho-oh is uber mostly thanks to this.
- Sludge Bomb = Poison-types are a bit more viable thanks to this.
- Crunch = Good move for the good Dark-types, but 80BP is just not enough for them.
- AncientPower = An alternative to the common Rock Slide or Hidden Power Rock, good.
- Giga Drain = A good move, 60BP is usable, and recovering your damage is great.
- Bonemerang = A Earthquake clone that break substitutes, good for Marowak.
- Pursuit = Pseudo-trapping was created with this, and was an useful move.
- Thief = Leafovers was on everything, and this can truly change the course of the battle there.
- Rapid Spin = Spikes was created and used a lot, so, a counter was needed.
- Hidden Power = 70BP of any type, an awesome unlimited coverage move.
- Return = 102BP to Normal-types, nice.
- Frustration = Same as adove.
Let's see, Heracross' Megahorn was incredible, but Heracross weren't never the best Pokémon of the game. Cross Chop was made Figther finally viable, and that is great, as they are important now, specially Machamp, but even then, they still fail at being the best. Marowak was a huge threat, but Earthquake is still usually better than Bonemerang. Pursuit was new, and good, nobody did too much damage with it, making it sometimes hard to use to the success. Rapid Spin can help you with Spikes, that will also help you to futher stalling, but this doesn't work on offensive teams too well. Return/Frustatin are great, but Body Slam tends to be more useful.
So, Hidden Power is maybe the most important offensive move for GSC and created on GSC, almost the 20-30% of the Pokémon use it to improve their coverage, so, yeah, that's really important, specially on some legendaries. And some even use it to get a STAB, too...
GSC (Support)
- Attract = One of most used moves by annoyers, specially without Evasion Clause.
- Baton Pass = This move created one of most powerful archtypes, and is useful as alone, too.
- Belly Drum = Wow, this thing really shaped GSC a lot.
- Charm = A great move for those passive Pokémon like Umbreon.
- Curse = Wow, this thing also shaped GSC a lot.
- Encore = Used a lot by annoyers, and it works really well.
- Heal Bell = Wow, this thing shaped a lot GSC, too, healing the status of the time? I'm in.
- Mean Look = Trapping was good by those times, specially with Perish Song.
- Milk Drink = Milktank was good thanks to this (in part).
- Moonlight = An useful move, but more used on lower tiers, still great.
- Morning Sun = Same as adove.
- Perish Song = PerishTrapping was a powerful tactic, wallbreaking everything.
- Roar = Phazing was created, and was spamed since then.
- Sandstorm = Used more when Evasion Clause din't existed, for passive damage.
- Sketch = Best move of the game, too bad Smeargle is awful.
- Sleep Talk* = This thing also shaped a lot GSC.
- Spikes = An important move, not used all the time, but it's really effective.
- Synthesis = Same as Moonlight.
- Whirlwind = Same as Roar.
Wow, this's hard to tell, if we look at the future, maybe Baton Pass, but here, on GSC, Belly Drum, Curse, Sleep Talk, Spikes, Heal Bell, Roar and Whirlwind were almost a mini-game inside of the main battle, but that mini-game were the most important thing on each battle, and when you losed the control of that game, you just losed. If I have to say one, I could say Roar/Whirlwind, why? Simple, huge boosters like Sword Dance always existed, but now with Roar/Whirlwind you can phaze them, you can finally force at total power a switch, that power is so important that almost any team carries at least one phazer, not just for Snorlax, but rather for almost the complete metagame.
Spikes helped a lot the phazing, but that was not so-vital as phazing alone. Baton Pass was powerful, but you needed at least two turn to start a chain, that is a lot of time, and thus, was more a thing of high risk, high reward stuff. Curse was omnipresent, but actually not that important was were RestTalking, it was more a sort of counter move that other thing. Sleep Talk with Rest almost shaped GSC, but, even then, Sleep Talk by alone was not SO important as Rest alone, Sleep Talk just made things faster and less prone to luck. Heal Bell was great, but it's not so easy to use as make it vital. And Perish Song was great, but not flawless or easy to use.
ADV (Attacks)
- Focus Punch = Needs prediction or a subsitute, but it's power is awesome.
- Overheat = Good last punch for some Pokémon.
- Superpower = A lot of power and without need of anything else, good.
- Volt Tackle = Great move, too bad it's just for Pikachu.
- Meteor Smash = Excelent move, bad type, but Metagross is great.
- Dragon Claw = Good option for Dragons, but that's pretty much all.
- Leaf Blade = Sceptiles' Signature is a pretty good move.
- Fake Out = Good for scouting, and scouting is a need.
Not too much stuff here... maybe Focus Punch is the best move introduced and used, and mostly to break some important walls like Tyranitar, but that's pretty much all, important, but not really vital. Fake Out deserve a special mention for doubles, it was and is still an important move there, too.
ADV (Support)
- Aromatherapy = Heal Bell clone, more variety with Clerics.
- Bulk Up = A better Curse, not bad, but that's pretty much all.
- Calm Mind = Maybe the best move of the game, some monster did born with this.
- Dragon Dance = Not omnipresent, but great eitherway.
- Helping Hand = Important on doubles.
- Memento = A good support move, it's not hard to start a sweep with this.
- Snatch = Great if you predict OK, but that's pretty much, high risk, high reward.
- Stockpile = Shaky distribution, but still a good move.
- Tail Glow = Great move, too bad Volbeat is not that good...
- Taunt = An important move should be said, it shaped somewhat the metagame.
- Will-O-Whisp = Other important move that shaped a bit the metagame.
- Yawn = Flawless sleep and seudo-phazing.
Obviously the best move is Calm Mind, but Dragon Dance, Taunt, and Will-O-Whisp are pretty near, anyway, you can really cripple stuff with just Taunt or Will-O-Whisp and sweep with Dragon Dance, but Calm Mind is more safer, someone heard of Suicune?