I got you the first time; I have other priorities at this point in time.
Anyway (Exams were a thing that needed to be dealt with beforehand which explains the delay):
Name: Eevee - Vaporeon
Availability: Eevee can be found in the grass in Castelia City with a 5% chance.
Stats: Vaporeon is quite bulky with nice HP and Special Defense; it can also utilize its high Special Attack. It is, however, quite slow.
Typing: Pure Water-typing comes with two weaknesses in Grass- and Electric-type attacks, while it offers good offensive coverage.
Movepool: Very shallow. Vaporeon needs Aurora Beam for coverage so it is worth relearning if missed. Surf is obtainable from Cheren on Route 6. Work Up is a good boosting move. It learns Ice Beam, Blizzard, and Shadow Ball through TM.
Major Battles: Vaporeon can be used against Clay and its Ice coverage against Drayden. Can be used against some of Iris' Pokemon as well.
Additional Comments: It is recommended to complete one streak in the Battle Subway (Multi Train with NPC partner is the easiest) to quickly gain the Battle Points for a Water Stone.
Changes
-Added some of MellowBusiness' and Conni's suggestions
-Minor rewrites
Name: Elekid
Availability: Elekid can be found in the Virbank Complex interior with a 25% chance. [White 2]
Stats: Elekid and its evolutions are reasonably fast and have good attacking stats, so you can utilize both physical and special attacks.
Typing: Pure Electric-typing means that it is only weak to Ground-types. It can also beat up on Flying- and Water-types.
Movepool: It learns many Electric-type moves like ThunderPunch, Discharge, and Thunderbolt. Many of its best TM moves come late but it can make use of Return, Psychic, Flamethrower. You can also tutor it Ice Punch with the ten free Red Shards for coverage.
Major Battles: Even with Ice Punch, Electabuzz struggles in Clay's gym. However, it bounces back against Skyla. Marlon is even easier, especially if you traded right away to evolve into Electivire. If you have Ice Punch, it can do well against Iris.
Additional Comments: If you have access to trading it is worth evolving to Electivire; however, if you don't, Electabuzz is still good. It actually has higher Speed than its evolution and can abuse Eviolite.
Changes
-Minor rewrites
Name: Lillipup
Availability: Lillipup can be found in Floccesy Ranch with a 40% chance.
Stats: Very decent for a Pokemon you get early in the game, with above average bulk, an average Speed stat, and a pretty powerful Base 100 Attack in its final form.
Typing: Normal-typing gives you good neutral coverage offensively and a lone weakness to Fighting-types defensively. An immunity to Ghost-types is very nice.
Movepool: Lillipup comes with a very good level-up movepool with Tackle and Bite early on, Crunch and Work Up coming not too far afterwards, and the elemental fangs later on in the game via Heart Scales. Dig and Return stand out as notable TM's to teach Lillipup, and Superpower via Move Tutor.
Major Battles: With the exception of Marshal, there is no matchup in the game that stands out as terrible for Lillipup. Against virtually every matchup, Lillipup will be able to reliably make a decent contribution towards the battle, especially in the early gyms, whether it be taking hits or dishing out the damage.
Changes
-Minor rewrites
Name: Litwick
Availability: Litwick can be found in Celestial Tower's 1st Floor with a 100% chance.
Stats: Litwick starts with terrible speed and mediocre bulk. Once it evolves, it has amazing special attack, alongside passable bulk and speed.
Typing: It has good STABs to work with, and a nice immunity to work with. Fire-typing complements Ghost's inability to hit Steel-types well.
Movepool: Comes with Flame Burst and a Hex + Will-O-Wisp combo. Shadow Ball, Fire Blast, Energy Ball, and Calm Mind are all good TMs to teach it.
Major Battles: Easily KOes most normal trainers after evolution, but does not shine particularly against the remaining Gyms or the Elite Four. Only advantageous match is versus Caitlin, but be careful of Shadow Ball on Gothitelle and Sigilyph. Colress goes down easily from its firepower.
Changes
-Placed more attention to the Litwick phase since it is relevant for a good 8-14 levels.
-Minor rewrites
Name: Oshawott
Availability: Oshawott is one of the three starters you pick from at the beginning of the game.
Stats: Balanced stats across the board, with some emphasis in Attack and Special Attack.
Typing: Water-typing gives it a nice variety of options, but it does not give Oshawott a lot of strong matchups throughout the game.
Movepool: Oshawott gets interesting movepool options, most notable being Megahorn from the move relearner (or X-scissor from TM), Superpower from move tutor, and Ice Beam and Blizzard from TM. It also gets Swords Dance, allowing it to pull off sweeps on some foes.
Major Battles: Oshawott is one of the best options against Clay, an otherwise difficult battle. Its coverage options make it a strong pick for Drayden as well. In the Pokemon League, it shines as a backup to almost everything, with a strong varied movepool to pick off weakened teams.
Changes
-Minor rewrites
Name: Petilil
Availability: Petilil can be encountered in the grass in Castelia City with a 35% chance in White 2 or can be traded for on Route 4 in Black 2.
Stats: Lilligant has a high base 110 Special Attack, which is supported by a solid base 90 Speed.
Typing: Grass is not a particularly good type because several common types resist it. It also has five weaknesses, although resistances to Ground and Water are quite helpful.
Movepool: Lilligant has a thin movepool with limited coverage, but it has everything it needs to work. As a Petilil, it has early access to decent STABs in Magical Leaf and Giga Drain. After that, Petilil has no particularly important moves, so you can evolve it early to gain Quiver Dance at level 28. At level 46, it learns Petal Dance, which makes it an even better sweeper.
Major Battles: Lilligant works best against Elesa, Clay, and Marlon. Its typing isn't particularly helpful against the other Gyms or the Elite 4.
Additional Comments: Petilil can be evolved with the Sun Stone obtained in Nimbasa City, but waiting until Level 28 for Quiver Dance is recommended. Own Tempo is recommended to prevent Petal Dance confusion, which the traded Petilil comes with.
Changes
-Minor rewrites
Going from Pidove next time.