Location: Pewter City
Gym Leader: Brock
Specialty: Rock-type
Reward: Boulder Badge, TM34, Can use HM05 - Flash

Puzzle:
This gym is fairly straightforward, with a direct walk to the leader. The only trainer in the gym uses two Ground-types, Sandshrew and Diglett, while the leader Brock uses Rock-types. Beware of his specialty move Bide, which absorbs damage for two to three turns then deals it back double to the enemy. Onix can be a bit of a pain since it's probably at a higher level than anything you have, and has decent defense. Bulbasaur and Squirtle can finish both Pokemon with a Bubble or Vine Whip, but Charmander may need to call in help from an ally like Butterfree. Naturally, the parting gift from Brock is TM34 Bide. You can now use Flash outside of battle.

Gym Leader Brock	Geodude	Onix
Battle Type Single Battle Items	Level 12	Level 14
	Attacks: Tackle Defense Curl	Attacks: Tackle Screech Bide Bind

Location: Cerulean City
Gym Leader: Misty
Specialty: Water-type
Reward: Cascade Badge, TM31, Can use HM01 - Cut

Puzzle:
Two trainers will challenge you on the way to Misty, one of whom you can skip. The other, who must be faced, has a Goldeen with the powerful Horn Attack move, so watch out. Again, we have a straightforward path to the Leader, along a pool filled with water. Later in the game you can come back and fish for Pokemon in the water if you so please. As for Misty herself, she uses two Pokemon from the same family - Staryu and Starmie. Staryu can be taken out no problem but Starmie will be a pain as Misty likes to use X Special on it in the beginning. It'll sometimes try to use harden to raise its Defense as well, so get it out of the way fast. Ivysaur or Pikachu both have awesome type coverage over it, Butterfree can use Stun Spore or Sleep Powder to dispatch it, and Clefairy or Jigglypuff can learn Thunder Wave by TM to paralyze it. Starmie likes to use Bubblebeam once it's set up, which can reduce Speed, so watch out. Though the move isn't terribly powerful it can be annoying when Starmie has +1 and already boasts incredible base Special as is. The secondary prize from her is TM11 Bubblebeam. You can now use Cut outside of battle.

Gym Leader Misty	Staryu	Starmie
Battle Type Single Battle Items	Level 18	Level 21
	Attacks: Tackle Water Gun	Attacks: Tackle Water Gun Harden Bubblebeam

Location: Vermillion City
Gym Leader: Lt. Surge
Specialty: Electric-type
Reward: Thunder Badge, TM24, Can use HM02 - Fly

Puzzle:
To get to the gym you first need to have acquired Cut from the S.S. Anne to knock down the bush blocking the path. This electrifying gym has an interesting novelty - you need to check for two switches hidden in the garbage cans to open the automatic doors. The second is always next to the first, be it the can north, south, east, or west, but will be difficult anyways to find as the locks reset if you click on the wrong can. The trainers are all fairly easy to beat, however you made need to heal a few times should your Pokemon become paralyzed. Lt. Surge himself isn't that hard with the right Pokemon. If you caught a Nidoran and it's now either Nidorino or Nidorina, you may wish to consider the final stage of evolution via Moon Stone to gain the Ground-type immunity to Electric. If not, Diglett's Cave is east of Vermilion and you can nab the elusive Diglett or its evolution Dugtrio to give you a hand. Surge's Voltorb has Sonicboom which will always deal 20 points of damage, so bring plenty of Super Potion. Pikachu isn't very tough but can paralyze. Raichu is extremely dangerous without a type immunity to Electric due to its Thunderbolt attack (which has the highest base power of any move yet in the game), so take incredible caution. The prize for this match is TM24 Thunderbolt. You can now use Fly outside of battle.

Gym Leader Lt. Surge	Voltorb	Pikachu	Raichu
Battle Type Single Battle Items	Level 21	Level 18	Level 24
	Attacks: Tackle Screech Sonicboom	Attacks: Thundershock Thunder Wave Growl Quick Attack	Attacks: Thunderbolt Thundershock Thunder Wave Growl

Location: Celadon City
Gym Leader: Erika
Specialty: Grass-type
Reward: Rainbow Badge, TM21, Can use HM04 - Strength

Puzzle:
Erika's gym requires Cut! The gimmick in this gym isn't actually that hard, just cut down trees to open the path to the leader. The gym trainers might force you to go back to the Pokemon Center a few times because of status conditions - stock up on healing items at the fabulous Celadon Department Store. Ultimately you don't need to fight all the trainers; 3 or 4 will do to be gain access to Erika depending on the path chosen. The battle with Erika might be tough but for once Charmander will prove to be a worthwhile choice in starter - attacks like Ember and Flamethrower will burn down her team. Be careful of Tangela's Bind: in this generation you won't be able to move while it's in use and if she's faster than you you're out of luck. Her Vileplume uses the self-healing move Mega Drain, which is also handed out via TM21. If you have Psychic-type moves on a Kadabra or Drowzee, I suggest breaking them out for Vileplume and Victreebel. After winning, you can use Strength outside of battle.

Gym Leader Erika	Victreebel	Tangela	Vileplume
Battle Type Single Battle Items	Level 29	Level 24	Level 29
	Attacks: Wrap Poisonpowder Sleep Powder Razor Leaf	Attacks: Bind Constrict	Attacks: Poisonpowder Mega Drain Sleep Powder Petal Dance

Location: Fuchsia City
Gym Leader: Koga
Specialty: Poison-type
Reward: Soul Badge, TM06, Can use HM03 - Surf

Puzzle:
Koga's gym is a maze of invisible walls. The floor that appears like dotted lines will always be solid so navigate through the floor where the lines are continued. The gym trainers are peculiar here, using a mix of Ground, Psychic, and Poison-types, despite only the former being used by Koga himself. Koga's team is fairly straight-forward - you've encountered most of this if you took the Cycling Road route and faced trainers there. Since Gen I doesn't have abilities, you can pelt Koffing and Weezing with Ground-type attacks, so if you brought along a Cubone or Sandslash it'll definitely be useful. Only Weezing uses Toxic (which badly poisons you), but everything can poison you so beware. The prize for this match is TM06 Toxic. If you have Venusaur, give it Leech Seed and Toxic as the effects of both in this generation will stack in a way that your enemies die much faster. After this match you can use Surf, the last of the HM moves which can be found at the back house of the Safari Zone.

Gym Leader Koga	Koffing	Muk	Koffing	Weezing
Battle Type Single Battle Items	Level 37	Level 39	Level 37	Level 43
	Attacks: Tackle Smog Sludge Smokescreen	Attacks: Disable Poison Gas Minimize Sludge	Attacks: Tackle Smog Sludge Smokescreen	Attacks: Smog Sludge Toxic Selfdestruct

Location: Saffron City
Gym Leader: Sabrina
Specialty: Psychic-type
Reward: Marsh Badge, TM46

Puzzle:
Only accessible after the Rockets have been defeated, Sabrina's gym is a network of, you guessed it, teleporters. Have fun trying to navigate through this mess. Here's a hint - you will need to battle a few of the trainers, who use a combination of Psychic-types and Ghost-types. Slowbro and Mr. Mime are both favourite choices amongst the trainers. Sabrina's team itself uses three pure Psychic-types and a Bug/Poison-type, Venomoth, which can confuse you with Psybeam or poison or paralyze with dual powder moves. Kadabra and Alakazam both have horrid defenses so try to use attacks that fall under the physical category of types, but watch out - Alakazam is very fast and will use Reflect for support to double its defense. The TM for this match is TM46 Psywave, a move that randomly multiplies the enemies level and damages it accordingly.

Gym Leader Sabrina	Kadabra	Mr. Mime	Venomoth	Alakazam
Battle Type Single Battle Items	Level 38	Level 37	Level 38	Level 43
	Attacks: Disable Psybeam Recover Psychic	Attacks: Confusion Barrier Light Screen Doubleslap	Attacks: Poisonpowder Leech Life Stun Spore Psybeam	Attacks: Psybeam Recover Psywave Reflect

Location: Cinnabar Island
Gym Leader: Blaine
Specialty: Fire-type
Reward: Volcano Badge, TM38

Puzzle:
After finding the hidden key to the Cinnabar Gym in Cinnabar Mansion, you'll be able to take a crack at Blaine's Fire-type madness. The gym puzzle is fairly straightforward - talk to the computers in the corner to be asked a question, and answer it right to move ahead. If you answer it wrong or don't want to do it at all, you'll have to fight the trainers to open the door. They use powerful Fire-types such as Ninetales and Charmander to wear you down. The head honcho himself uses four powerful Fire-types, two basic form and their evolutions, which use a mixture of Fire-type and Normal-type attacks. Watch out for Ponyta and Rapidash's Fire Spin; should they hit you with it you will be trapped and unable to fight back or switch, and if they're faster than you they'll continue to use it until you're down for the count. Ground-types, Water-types, and Rock-types you may have used in the previous gyms will come in very handy here. The prize for this match is TM38 Fire Blast, which Blaine's Arcanine uses in the fight to inflict massive damage and the crippling Attack-reducer status burn. Ha! You better have Burn Heal!

Gym Leader Blaine	Growlithe	Ponyta	Rapidash	Arcanine
Battle Type Single Battle Items	Level 42	Level 40	Level 42	Level 47
	Attacks: Ember Leer Take Down Agility	Attacks: Tail Whip Stomp Growl Fire Spin	Attacks: Tail Whip Stomp Growl Fire Spin	Attacks: Roar Ember Take Down Fire Blast

Location: Viridian City
Gym Leader: Giovanni
Specialty: Ground-type
Reward: Earth Badge, TM27

Puzzle:
The mysterious gym you passed by at the start of your adventure is now ready to be faced...and it's home to none other than your old nemesis Giovanni! The puzzle in this gym is another of those confusing arrow spinning mazes like in his Rocket Game Corner hideout. It's a real hassle but in the middle of the gym there's a Revive waiting for you should you need it. The trainers here are not Rocket Grunts but in fact Cooltrainers, Black Belts, and Jugglers: they also use a wide variety of Pokemon types including Normal, Poison, Fighting, and Rock. However, the main focus here is still Ground-types. Giovanni himself will try to bring you down in a plethora of ways; he'll mix brawn with brains, status with raw power, and whittling you down with direct one hit knockout. His Rhydon, a fearsome Pokemon on its own merit, uses two OHKO attacks, Fissure and Horn Drill: if they hit you, your Pokemon is down for the count. Dugtrio's Sand-Attack coupled with already ferocious Speed is extremely annoying, and Nidoqueen's dual status inducing set of Poison Sting and Body Slam can give you trouble for days if you don't pack Full Heals. Give this team a taste of Water-type moves: while Grass-type moves are handy for Rhyhorn and Rhydon, they are nulled by Nidoking and Nidoqueen, whereas a solid Surf or Hydro Pump can sweep his entire team just as well. The prize for this match is both entry to Pokemon League and TM27 Fissure, the nightmarish OHKO move used on you in this match. Save it for the Pokemon League!

Gym Leader Giovanni	Rhyhorn	Dugtrio	Nidoqueen	Nidoking	Rhydon
Battle Type Single Battle Items	Level 45	Level 42	Level 44	Level 45	Level 50
	Attacks: Stomp Tail Whip Fury Attack Horn Attack	Attacks: Growl Dig Sand Attack Slash	Attacks: Scratch Tail Whip Poison Sting Body Slam	Attacks: Tackle Horn Attack Poison Sting Thrash	Attacks: Stomp Tail Whip Fissure Horn Drill