Electabuzz (Red only) -
Mid Tier
Availability: Late (Power Plant)
Stats: Above average Attack for an Electric-type. Nothing else of note.
Movepool: Learns Thunderpunch, which is an acceptable TM24 substitute if you already used it. Interestingly, it learns Submission and Psychic via TM.
Power: Electric STAB is great for when you get it, due to the abundance of Swimmers at that point in the game. Submission and Psychic mean that it's the one of the few Electric-types in the game that doesn't have to worry too much about Ground-types.
Type: As noted previously, Electric is a very good typing for this point in the game, with the only weakness being Ground, which you only have to worry about in Viridian City.
Match-ups:
Sabrina: It can beat most of her Pokemon 1-on-1, but don't try to take out her entire team with it.
Blaine: Not too bad. Watch out for Arcanine, as it knows Take Down. Rapidash can also be annoying due to Fire Spin.
Giovanni: He's not much trouble, as Psychic dispatches the Nidos and the only Pokemon on his team that knows a Ground move is Dugtrio.
Lorelei: Most of her team can be easily 2HKOed by Thunderbolt/punch. Jynx and Lapras can both survive a hit and retaliate with Lovely Kiss or Body Slam, respectively.
Bruno: Whether you do well or poorly against him depends on whether you taught it Submission/Psychic. Simply put, you can beat his 2 Onix with either Submission or Psychic, but keep Submission's recoil in mind. Hitmonchan is easily beaten with just Thunderbolt/punch, but you'll need Psychic to (somewhat) reliably beat Hitmonlee and Machamp.
Agatha: Golbat is easily OHKOed with your Electric move of choice, but you'll want Psychic to beat the rest of her team, but watch out for Hypnosis from her Haunter and first Gengar.
Lance: Thunderpunch/bolt OHKOes Gyarados and Aerodactyl, but attacking Aerodactyl isn't recommended due to its massive Speed and access to Hyper Beam. The rest of his team can handily deal with Electabuzz, so don't use it against them.
Additional Comments: While it may seem outclassed by other Electric-types, such as Pikachu and Zapdos, Electabuzz is by no means a bad Pokemon, thanks to the fact that it's one of only 3 Electric-types that can notably damage Ground-types.
Resubmitting
Magmar, because my original submission was very bare-bones.
Magmar (Blue only) -
Bottom Tier
Availability: Very Late (Pokemon Mansion)
Stats: It has the second highest Attack of any Fire-type you can use when you get it (Flareon says hi). Everything else is what you'd expect from a Fire-type.
Movepool: The fact that it can learn Psychic, Submission, and Confuse Ray often makes one forget that it only knows Ember when you catch it, meaning that it'll generally be reliant on TMs until it gets to Lv.
43 and learns Fire Punch.
Power: Ember alone isn't going to win you any fights, meaning that you'll have to either waste Psychic/Submission on it or grind it up to Lv. 39, when it learns Confuse Ray, for it to start pulling its weight in battle.
Type: Fire is a very bad type late-game, due to the multitude of Pokemon that resist it.
Match-ups:
Blaine: As mentioned previously, Ember alone isn't going to win you any fights, and Blaine is no exception, as all of his Pokemon resist it, while they can put the hurt on Magmar with Take Down/Stomp.
Giovanni: While Ground is SE against Magmar, the only Pokemon that know moves of that type are Dugtrio, who's faster and would win if it uses Dig, and Rhydon, who's too slow to use Fissure effectively. Psychic takes care of the Nidos.
Lorelei: The only Pokemon she has that doesn't resist Fire can put Magmar to sleep.
Bruno: Handily beaten if Magmar knows Psychic. Watch out for Hi Jump Kick and Submission, however.
Agatha: Same as Bruno, but 2 of her Pokemon can Hypnosis you, and those 2 are faster than Magmar.
Lance: No. All of his Pokemon resist Fire and can beat Magmar 1-on-1.
Additional Comments: Magmar is a case of being at the wrong place at the wrong time with the wrong skills. While it
can harm Rock-types, they aren't exactly common at the time you get it. If it could be caught earlier and learned Fire Punch and Confuse Ray earlier, it might be worthy of recognition, but it doesn't, and that is why Magmar is Bottom of the barrel.
Also resubmitting
Sandshrew. I feel that I did a very poor job in submitting it by constantly comparing to Geodude and mentioning Slash only once.
Sandshrew (Blue/Yellow only) -
High Tier
Availability: Early, Route 4 (Route 3 if you're playing Yellow). Evolves at Lv. 22.
Stats: Good Attack and Defense, at the cost of Special and Speed.
Movepool: Learns Slash as early as Lv. 17. Also learns Swords Dance and Rock Slide via TM. Unfortunately, it can't learn any Ground-type moves by level-up.
Power: Slash and its massive crit rate allow it to OHKO/2HKO almost everything that doesn't resist it, and whatever does is hit Super-Effectively by Dig. This, combined with its somewhat-early evolution allows it to absolutely destroy the early-game trainers. Keep in mind, however, that its low Speed means that it usually has to take a hit before it can attack, and special attacks, especially SE ones, destroy it.
Type: Mono-Ground typing is a double-edged sword; on one hand, it has no physical weaknesses, and the multitude of Poison-types in the game are an ample supply of experience for it. On the other hand, it has only 2 resistances, only 1 of which is special, and it has a weakness to Water, a very common type late-game.
Match-ups:
Misty: She beats Sandshrew even if it was hit neutrally by Water.
Lt. Surge: He gets destroyed.
Erika: 2 of her Pokemon are weak to Dig, but they're both faster than you and know Mega Drain/Razor Leaf.
Koga: Puts up a good fight, but is still easily beaten.
Sabrina: Even though she doesn't have a type advantage, the overall dominance of the Psychic type gives her a guaranteed victory.
Blaine: Fire's a special type, and his Rapidash knows Fire Spin, making fighting him with Sandslash inadvisable.
Giovanni: 4 (3 in Yellow) of his Pokemon are weak to Ground, despite being the Ground-type Gym Leader. His Pokemon also know no special attacks whatsoever (minus the ineffective Thunder), further encouraging Sandslash to tank him.
Lorelei: Do I have to elaborate on how she beats Sandslash?
Bruno: His 2 Onix are demolished by Earthquake, and Sandslash's high Defense allows it to take a Hi Jump Kick from Hitmonlee, or a Submission from Machamp.
Agatha: While her entire team (minus Golbat) is vaporized by EQ, all of them are faster and can Confuse/Hypnotize/Psychic Sandslash.
Lance: 3 of his Pokemon are immune to Ground. Aerodactyl and even Dragonite can be beaten 1-on-1 thanks to Rock Slide, but Gyarados knows Hydro Pump, which easily OHKOes Sandslash. In Yellow, the only ones Sandslash can beat are his Aerodactyl and first Dragonair.
Additional Comments: Sandshrew is a great in-game physical tank, and Slash combined with Dig allows it to plow through early game, as well as Team Rocket. Its poor Speed and weakness to Water are its main flaws.