Articuno

Availability: Late-game (Seafoam Island, level 50).
Typing: Ice/Flying-type is a good combination, being super effective against Giovanni and Lance and neutral elsewhere outside of Blaine and Lorelei.
Stats: Articuno has great all around, having above-average Speed, being powerful and really bulky.
Movepool: When caught, Articuno has Ice Beam. The Fly HM can also be used for utilities outside of battle but Articuno will rarely use it.
Major Battles: Articuno sweeps Sabrina and Giovanni and does extremly well against Lance. It's mostly good in other major battles, being ble to take down a few foes, with the exception of the Blaine's and Lorelei's fight.
Additional Comments: Articuno is a great Pokemon that comes at a very high level that performs really well without needing contested TM, only held back by its late arrival. Catch it with a Master Ball as catching it with other types of Poke-Ball is too time-consuming.

Availability: Late-game (Seafoam Island, level 50).
Typing: Ice/Flying-type is a good combination, being super effective against Giovanni and Lance and neutral elsewhere outside of Blaine and Lorelei.
Stats: Articuno has great all around, having above-average Speed, being powerful and really bulky.
Movepool: When caught, Articuno has Ice Beam. The Fly HM can also be used for utilities outside of battle but Articuno will rarely use it.
Major Battles: Articuno sweeps Sabrina and Giovanni and does extremly well against Lance. It's mostly good in other major battles, being ble to take down a few foes, with the exception of the Blaine's and Lorelei's fight.
Additional Comments: Articuno is a great Pokemon that comes at a very high level that performs really well without needing contested TM, only held back by its late arrival. Catch it with a Master Ball as catching it with other types of Poke-Ball is too time-consuming.
Magikarp

Availability: Early-game (Route 3 Pokemon Center for 500 Poké Dollars at level 5).
Typing: Gyarados' Water/Flying-type is great, providing resistances to Misty, being super-effective against Blaine and Koga and only weak to Lt. Surge.
Stats: Gyarados has mostly great stats, boasting a really high Attack, great bulk and above-average Speed. However, its Special Attack is a bit lackluster.
Movepool: Gyarados learns Bite, Hydro Pump, Rain Dance and Dragon Dance by level up. Surf and Strength HM as well as Return TM are great options to use.
Major Battles: Gyarados wins against Misty, Koga, Sabrina, Blaine and Giovanni. It performs pretty well against the Elite 4, defeating Lorelei and Bruno thanks to Dragon Dance,while doing alright in other battles.
Additional Comments: In spite of how annoying it is to get Magikarp and the Slow level up, Gyarados is a great Pokemon to consider that will perform extremly well in most major battles. Intimidate is an useful ability that imrpoves Gyarados' bulk and allow it to use Dragon Dance on Bruno's Onix.

Availability: Early-game (Route 3 Pokemon Center for 500 Poké Dollars at level 5).
Typing: Gyarados' Water/Flying-type is great, providing resistances to Misty, being super-effective against Blaine and Koga and only weak to Lt. Surge.
Stats: Gyarados has mostly great stats, boasting a really high Attack, great bulk and above-average Speed. However, its Special Attack is a bit lackluster.
Movepool: Gyarados learns Bite, Hydro Pump, Rain Dance and Dragon Dance by level up. Surf and Strength HM as well as Return TM are great options to use.
Major Battles: Gyarados wins against Misty, Koga, Sabrina, Blaine and Giovanni. It performs pretty well against the Elite 4, defeating Lorelei and Bruno thanks to Dragon Dance,while doing alright in other battles.
Additional Comments: In spite of how annoying it is to get Magikarp and the Slow level up, Gyarados is a great Pokemon to consider that will perform extremly well in most major battles. Intimidate is an useful ability that imrpoves Gyarados' bulk and allow it to use Dragon Dance on Bruno's Onix.
Bellsprout

Availability: Early-game (Route 24, level 12-14) (LeafGreen).
Typing: Grass/Poison-type is great for Misty, Lt.Surge, Giovanni, Lorelei and Bruno but is a downside for Koga, Blaine, Agatha and Lance.
Stats: Victreebel is powerful on the physical and special side but it's rather frail and has middling speed.
Movepool: The Bellsprout line learns Growth, Vine Whip, Sleep Powder and Razor Leaf by level up. Once available, Sunny Day and SolarBeam TMs offer a really powerful STAB move. It's also possible to learn the Giga Drain TM.
Major Battles: The Bellsprout's line wins against Misty, Lt. Surge, Giovanni and Lorelei. However, in other major batles, it will mostly be useless, not taking down more than 1 foe with the exception of the Bruno's fight.
Additional Comments: Victreebel is a really situational Pokemon that either performs very well or can't do much. Chlorophyl is a great ability that let's Victreebel outspeed everything after it uses Sunny Day. Evolve Weepinbell with a Leaf Stone from Celadon Dept. Store after getting Razor Leaf at level 42.

Availability: Early-game (Route 24, level 12-14) (LeafGreen).
Typing: Grass/Poison-type is great for Misty, Lt.Surge, Giovanni, Lorelei and Bruno but is a downside for Koga, Blaine, Agatha and Lance.
Stats: Victreebel is powerful on the physical and special side but it's rather frail and has middling speed.
Movepool: The Bellsprout line learns Growth, Vine Whip, Sleep Powder and Razor Leaf by level up. Once available, Sunny Day and SolarBeam TMs offer a really powerful STAB move. It's also possible to learn the Giga Drain TM.
Major Battles: The Bellsprout's line wins against Misty, Lt. Surge, Giovanni and Lorelei. However, in other major batles, it will mostly be useless, not taking down more than 1 foe with the exception of the Bruno's fight.
Additional Comments: Victreebel is a really situational Pokemon that either performs very well or can't do much. Chlorophyl is a great ability that let's Victreebel outspeed everything after it uses Sunny Day. Evolve Weepinbell with a Leaf Stone from Celadon Dept. Store after getting Razor Leaf at level 42.
Oddish

Availability: Early-game (Route 24, level 12-14) (FireRed).
Typing: Grass/Poison-type is great for Misty, Lt. Surge, Giovanni, Lorelei and Bruno but is a downside for Koga, Blaine, Agatha and Lance.
Stats: Vileplume is a powerful Special Attacker that is fairly bulky, on the physical and special side. However, it's slow and will be outsped most of the time.
Movepool: The Oddish line learns Absorb and Sleep Powder by level up. The Giga Drain, once available is a stronger STAB move. Sunny Day and SolarBeam TMs offer a really powerful STAB move.
Major Battles: The Oddish's line wins against Misty, Lt. Surge, Giovanni and Lorelei. However, in other major batles, it will mostly be useless, not taking down more than 1 foe with the exception of the Bruno's fight.
Additional Comments: Vileplume is a really situational Pokemon that either performs very well or can't do much. Chlorophyl is a great ability that let's Victreebel outspeed everything after it uses Sunny Day. Evolve Gloom with a Leaf Stone from Celadon Dept. Store.

Availability: Early-game (Route 24, level 12-14) (FireRed).
Typing: Grass/Poison-type is great for Misty, Lt. Surge, Giovanni, Lorelei and Bruno but is a downside for Koga, Blaine, Agatha and Lance.
Stats: Vileplume is a powerful Special Attacker that is fairly bulky, on the physical and special side. However, it's slow and will be outsped most of the time.
Movepool: The Oddish line learns Absorb and Sleep Powder by level up. The Giga Drain, once available is a stronger STAB move. Sunny Day and SolarBeam TMs offer a really powerful STAB move.
Major Battles: The Oddish's line wins against Misty, Lt. Surge, Giovanni and Lorelei. However, in other major batles, it will mostly be useless, not taking down more than 1 foe with the exception of the Bruno's fight.
Additional Comments: Vileplume is a really situational Pokemon that either performs very well or can't do much. Chlorophyl is a great ability that let's Victreebel outspeed everything after it uses Sunny Day. Evolve Gloom with a Leaf Stone from Celadon Dept. Store.
Jolteon

Availability: Mid-game (Celadon Mansion, level 25 Eevee).
Typing: Pure Electric-type is good offensively, being Super-effective against Lorelei, only resisted by Erika and Giovanni and neutral elsewhere.
Stats: Jolteon boasts an excellent Speed, outspeeding everything, has a great Special and good Special bulk. However, it has a below-average Physical bulk.
Movepool: The Thunderbolt TM is required on Jolteon because it's a powerful STAB move. Rain Dance and Thunder TM can also be learned to provide a stronger STAB option.
Major Battles: Jolteon performs well against Koga, Sabrina and Blaine, although it doesn't outright win against the latter and can't do anything against Giovanni. Against the Elite 4, Jolteon has a good performance against Lorelei and Agatha and can take down a few foes weak to Electric-type.
Additional Comments: Jolteon is a decent Electric-type that does alright in major battles and easily defeats Water- and Flying-types. However, it really struggles against bulkier opponent like Bruno and won't do anything against Giovanni. It's also really reliant on the costly Thunderbolt TM because it's the only powerful STAB it can get.

Availability: Mid-game (Celadon Mansion, level 25 Eevee).
Typing: Pure Electric-type is good offensively, being Super-effective against Lorelei, only resisted by Erika and Giovanni and neutral elsewhere.
Stats: Jolteon boasts an excellent Speed, outspeeding everything, has a great Special and good Special bulk. However, it has a below-average Physical bulk.
Movepool: The Thunderbolt TM is required on Jolteon because it's a powerful STAB move. Rain Dance and Thunder TM can also be learned to provide a stronger STAB option.
Major Battles: Jolteon performs well against Koga, Sabrina and Blaine, although it doesn't outright win against the latter and can't do anything against Giovanni. Against the Elite 4, Jolteon has a good performance against Lorelei and Agatha and can take down a few foes weak to Electric-type.
Additional Comments: Jolteon is a decent Electric-type that does alright in major battles and easily defeats Water- and Flying-types. However, it really struggles against bulkier opponent like Bruno and won't do anything against Giovanni. It's also really reliant on the costly Thunderbolt TM because it's the only powerful STAB it can get.
Krabby

Availability: Mid-game (Vermillion City (Super Rod), level 15-25).
Typing: Pure Water-type helps Kingler against Blaine and Giovanni and is only resisted by Erika and Lorelei.
Stats: Kingler has a really high Attack and Defense as well as above-average Speed. However, it's really frail on the Special side and has a really Special Attack.
Movepool: By level up, Krabby learns Mud Shot at level 23. The Surf and Strength HM has uses outside of battles and provide a STAB and a powerful move respectively. Kingler can also learn the Rock Tomb and Ice Beam TM.
Major Battles: Kingler wins against Blaine and Giovanni and is mostly below-average elsewhere. It can get a few KOs in major battles but will never be able to contribute much.
Additional Comments: Krabby does well against Blaine and Giovanni but tend to not do much elsewhere due to its poor Special attack and bulk. However, it has some utilities by being able to fit the HM Strength and Surfin its moveset while still performing alright in battles.

Availability: Mid-game (Vermillion City (Super Rod), level 15-25).
Typing: Pure Water-type helps Kingler against Blaine and Giovanni and is only resisted by Erika and Lorelei.
Stats: Kingler has a really high Attack and Defense as well as above-average Speed. However, it's really frail on the Special side and has a really Special Attack.
Movepool: By level up, Krabby learns Mud Shot at level 23. The Surf and Strength HM has uses outside of battles and provide a STAB and a powerful move respectively. Kingler can also learn the Rock Tomb and Ice Beam TM.
Major Battles: Kingler wins against Blaine and Giovanni and is mostly below-average elsewhere. It can get a few KOs in major battles but will never be able to contribute much.
Additional Comments: Krabby does well against Blaine and Giovanni but tend to not do much elsewhere due to its poor Special attack and bulk. However, it has some utilities by being able to fit the HM Strength and Surfin its moveset while still performing alright in battles.
Meowth

Availability: Early-game (Route 5, level 10-16).
Typing: Pure Normal-type is neutral in most matchup, except for Bruno and Agatha.
Stats: Persian has a great Speed but below-average stats outside of it.
Movepool: By level up, Meowth gets Pay Day and Screech. The Return and Secret Power TM provide a great STAB and Shadow Ball may be use for the Agatha's fight.
Major Battles: Persian wins against Sabrina and does well against Agatha assuming it has Shadow Ball. It's mostly average in other major battles and will only get a few KOs with Screech + STAB.
Additional Comments: Despite its early arrival, Persian is a mediocre Pokemon performant-wise because of its low stats. However, it has some utilities outside of battle with Pay Day, generating money and Pickup as a Meowth to collect items.

Availability: Early-game (Route 5, level 10-16).
Typing: Pure Normal-type is neutral in most matchup, except for Bruno and Agatha.
Stats: Persian has a great Speed but below-average stats outside of it.
Movepool: By level up, Meowth gets Pay Day and Screech. The Return and Secret Power TM provide a great STAB and Shadow Ball may be use for the Agatha's fight.
Major Battles: Persian wins against Sabrina and does well against Agatha assuming it has Shadow Ball. It's mostly average in other major battles and will only get a few KOs with Screech + STAB.
Additional Comments: Despite its early arrival, Persian is a mediocre Pokemon performant-wise because of its low stats. However, it has some utilities outside of battle with Pay Day, generating money and Pickup as a Meowth to collect items.
Reserving Flareon, Geodude (trade and non-trade), Horsea, Poliwag, Rattata and Shellder.