I've done several runs now; so I'll post several pokemon. I've specifically been attempting to use pokemon that I expected would not be used as much.
Note these assume you are not using ther EXP Share, and thus you are not stupidly overleveled to the point everything may as well be S-Tier.
Fennekin/Braixen/Delphox: - A Tier
Availability: Starter
Stats:
[Estimated]
Fennekin: 40/45/40/62/60/60
Braixen: 59/59/58/90/70/73
Delphox: 75/69/72/114/100/104
In all forms, Delphox is a special attacker, with a much higher special bulk than physical bulk.
Typing: Fire/Psychic is an unusual type combination, and has several advantages, such as Fire dealing with Psychic's weakness to bug, and getting past Steel types. Offensively, the combination is magnificent, although Delphox is vulnerable to Ground, Rock, Water and Dark attacks.
Movepool: Delphox's movepool is it's major letdown. Even taking into account it's TM pool, it doesn't have much [usable] coverage outside of Psychic, Fire and Normal. In addition, Delphox suffers from a lack of good attack in the midgame. It's best moves until Lv 34 are Ember and STAB-less Psybeam. However, Delphox does get some support moves; most notably Light Screen; which makes it's role as a specially-based tank even more noticeable.
Major Battles:
Alexia - Can sweep the gym solo without any grinding beforehand
Grant - Useless. May get in a solo hit on Amaura; however.
Korrina - Average. Un-STAB'ed Psybeam isn't anything to write home about; although it may have Psyshock is you are overleveled
Ramos - A joke. Even if your best Fire STAB is Mystic Fire; Jumpluff is a joke, Weepinbel is a joke, and Gogoat isn't much better.
Clemont - Average. Mystic Fire's Sp.Atk drop comes in handy, and Delphox is useful against Magneton in particular.
Valerie - Solid. Between resisting Fairy, Mystic Fire and Light Screen, there is little Valerie can do as you wear her down.
Olympia - Average; Shadow Balls are annoying, but it can handle Slyglyph and Meowstic with Light Screen.
Wulfric - Click Flamethrower. Maybe mix it up with a Psyshock on Cryongal.
Team Flare - Useless. Dark and Fire types are very common in the Team Flare battles.
Rival - Carries two Dark types, one of which being part Water. Pretty bad.
Malva - Solid; as long as it stays away from Chandelure
Wikstrom - Sweeps
Dransa - Mine actually did decent here, Psychic handles Dragalge; and does a fair job on the rest of her team. Light Screen helps against Noivern.
Seibold - Keep away
Diantha - Very good. Only struggles with Goodra and Tyrantum. Mine actually 1v1'ed Mega Gardevoir and won [Thanks to Light Screen]
Additional Comments: Would probobly be S-Tier if the rival and Team Flare were not so happy with their Dark-types; or if it got a better fire move earlier. It's movepool is like G/S/C Cyndaquil's was, you're stuck with Ember forever.
Ducklett/Swanna: - B Tier
Availability: Route 7; moderately common. Evolves into Swanna at Lv 35
Stats:
Ducklett - 62/44/50/44/50/55
Swanna - 75/87/63/87/63/98
Ducklett and Swanna are both mixed attackers; and neither are too frail. Interestingly; Ducklett with Evolte is almost as bulky as Swanna.
Typing: Water/Flying is a great typing, both on the offense, and in terms of taking hits. Look at Gyarados!
Movepool: Swanna's movepool is basically Flying, Water and Normal; as well as several support or annoyance moves, like Featherdance; Roost; Rain Dance and Tailwind. However, it does get a wide range of useful Water and Flying STABs, unlike other Water/Flying types.
Major Battles:
Grant - Can deal with Amaura; but will lose to Tyrunt
Korrina - Depends if it has evolved or not. Evolved, it can rip through the gym. Unevolved; it's still solid, but probobly won't sweep. Featherdance is great here
Ramos - Sweeps
Clemont - Absolutely useless.
Valerie - Average; no advantage or disadvantage; although it cannot Featherdance things.
Olympia - Suffers a little against Slowbro; but can probobly take out either Silyglyph or Meowstic.
Wulfric - Not awful, but not great.
Team Flare - Excellent. Swanna destroys their fire-types, and beat pretty much anything else thrown at it, except Manetrics. This goes for the Admins and Lysandre as well. Swanna can defeat Mega Gyarados by using Featherdance, or just set up for something else to do so.
Rival - Best if you picked Froakie, good if you picked Chespin, average if you picked Fennekin.
Malva - Can sweep, although has to be careful of Stone Edge from Torkoal
Wikstrom - Can deal solid damage, and cripple some of his team with Featherdances
Dransa - Pretty useless outside Featherdance
Seibold - Unlike Lysandre's Gyarados, Swanna can't deal with his easily due to Dragon Dance
Diantha - Can defeat her Hawlucha, Aurous and Goltergheist.
Additional Comments: Swanna is a lot stronger in X/Y than B/W simply because it comes earlier. Ducklett coming when you can use a Sharp-Beak boosted Wing Attack is great for that point of the game. Also Surf is stupid early.
Klefki: - C Tier
Availability: Route 15/16, Lost Hotel. Hard not to find one
Stats:
Klefki - 57/80/91/80/87/75
No spectacular stats. It isn't too soft, isn't too slow, and isn't too puny, but doesn't stand out either.
Typing: Steel/Fairy is an amazing typing. It brings two immunities [Including to Poison Status]; while only having two weaknesses [Fire and Ground]. The STAB's have good coverage as well, although Steels pose problems.
Movepool: Klefki gets what it needs. Foul Play is a godsend and can really smash some physical attackers. Dazzlng Gleam will be avaliable on capture, and it knows Mirror Shot on capture.
Major Battles:
Olympia - Very useful, due to the Psychic resist, Foul Play can deal heavy damage to her Meowstic.
Wulfric - Solid,although Mirror Shot isn't the best attack, Klefki resists Ice.
Team Flare - OK. Struggles against Fire-types, but does well against Darks; and Golbats.
Rival - Can almost sweep them, unless you chose Chespin, and with the exception of their Eeveelution.
Malva - Useless
Wikstrom - Can OHKO Ageislash with Foul Play
Dransa - Excellent, although may have issues with Draglage
Seibold - Stats let Klefki down here
Diantha - Not great, although it can beat her fossils.
Additional Comments: Prankster is a great boon for Klefki. I personally ran Foul Play/Mirror Shot/Dazzleing Gleam/Attract on mine. Even if Klefki cannot defeat a pokemon itself, there's always Attracthax, or Thunder Wave. Would be D if not for good matchups in most boss fights after you obtain it.
Goomy/Sligoo/Goodra: - C Tier
Availability: Route 14
Stats:
Goomy: 45/50/35/55/75/40
Sligoo: 68/75/53/83/113/60
Goodra: 90/100/70/110/150/80
No spectacular stats. It isn't too soft, isn't too slow, and isn't too puny, but doesn't stand out either.
Typing: Even with the Fairy type; Pure Dragon is still great.
Movepool: Strange. Goomy's initial movepool is pretty awful; but Water/Dragon isn't bad coverage, and it quickly learns Muddy Water. It's movepool remains pretty bad until Goodra; by which time it had Dragon Pulse, and can be tutored Power Whip. Also has access to Boltbeam. Personally my Goodra ran Power Whip/Ice Beam/Dragon Pulse/Muddy Water
Major Battles:
Valerie - Absolute dead weight
Olympia - Average. Her team generally has decent Sp.Def as well. Mewostic might lose.
Wulfric - Bad, although it's high Sp.Def may let Goodra take an Ice Beam.
Team Flare - Pretty powerful, although dislikes physical attacks
Rival - Not outstanding, although it has the upper hand against all three starters
Malva - Can sweep easily
Wikstrom - Poor. Klefki is a Fairy, Probopass is useless; Ageislash and Scizor can deal massive damage
Dransa - Trade situations. Beats her special attackers, loses to her physicals
Seibold - Strong, and can deal with most of his team, although it may struggle with Gyarados
Diantha - Strong against a fair amount of her team, but is unlikly to take out all three that it can beat alone. Useless against Mega Gardevoir.
Additional Comments: Takes a hit for it's evolution condition; may have been B otherwise. It's a powerhouse once it's evolved, and Sligoo is pretty solid in itself provided you keep it away from physical attackers. [And by that point it should be hogging Evolite anyway]
Bulbasaur/Ivysaur/Venusaur/Mega Venusaur: - S Tier
Availability: Shortly after the 1st badge
Stats:
Bulbasaur: 45/49/49/65/65/45
Ivysaur: 60/62/63/80/80/60
Venusaur: 80/82/83/100/100/80
M.Venusaur: 80/100/123/122/120/80
Venusaur is a slow tank with the ability to unleash solid attacks on both sides of the spectrum, although it leans towards the special side [Except in it's Mega Form; where it's defense is higher physically]
Typing: Grass/Poison isn't the world's greatest typing; but it's solid. Gets a lot stronger with Thick Fat.
Movepool: Venusaur's movepool isn't wide, but it is exceptionally useful. Due to early access to PoisionPowder and Venoshock, Bulbsaur/Ivysaur almost immediately gets a Base 65 STAB; which becomes a Base 130 STAB on a poisoned target. This is simply unmatched power in the early game, as the only other pokemon capable of STAB Boosted Venoshock at this point have far less sp.atk [Gulpin and Beedrill. Roselia is unlikely to be obtained without grinding for happiness at this point.]
When it comes to Grass STAB there are 3 main options, Petal Dance; Grass Pledge and Petal Blizzard.
Major Battles:
Grant - Can deal with Amaura; but will lose to Tyrunt
Korrina - Depends if it has evolved or not. Evolved, it can rip through the gym. Unevolved; it's still solid, but probobly won't sweep. Featherdance is great here
Ramos - Sweeps
Clemont - Very strong. Can sweep if it has Bulldoze.
Valerie - Venoshock
Olympia - Can beat Slowking
Wulfric - Can MegaEvolve and win.
Team Flare - Poor, due to weakness to fire.
Rival - Average; and sytarter-dependant.
Malva - Has to sit out
Wikstrom - Sits out, unless it knows Earthquake/Bulldoze
Dransa - Not useless, as it can get off Venoshocks.
Seibold - Sweeps
Diantha - Not that useful in this fight, unfortunetly. Usefulness varies based on moveset, from 'Useless' to 'Can possibly beat one or two'.
Additional Comments: This thing is stupid. I'd actually say it's better than Squirtle and Charmander, simply because of the raw power behind it's STAB moves early. Having STAB Venoshock and the means to trigger it's boost before it even evolves is just stupid. And Petal Dance isn't much better.
My Venusaur literally never even got down to red HP at any point in the game
Also, Razor Leaf for murdering early hordes to powerlevel, and Petal Blizzard for later ones.
Absol: - B Tier
Availability: Route 8
Absol: 65/130/60/75/60/75
Absol is a glass cannon; it's speed is middleing.
Typing: Pure Dark; not great, not bad.
Movepool: Absol has a pretty wide movepool; rangeing from support or utility moves such as Taunt, to Swords Dance; to powerful physical moves such as Night Slash; Psycho Cut and X-Scissor; to even a respectable special movepool. You'd think Absol was a Normal-type with it's movepool.
Major Battles:
Grant - Sweeps the Gym with Rock Smash coming off Base 130 Atk.
Korrina - Useless
Ramos - Can probobly sweep the gym because this guy is a joke, but I didn't use it.
Clemont - Can deal a lot of damage with it's attacks
Valerie - Bad
Olympia - Sweeps
Wulfric - Can deal with everything but the iceburg.
Team Flare - Average; becomes bad when they start using Scrafties and Houndooms.
Rival - Crushes their Mewostic lead.
Malva - Can beat Chandelure
Wikstrom - Annoyingly Sucker Punch hits Ageislash while it's still in Sheild Forme, so Absol is pretty bad here
Dransa - Can land powerful hits on her slower dragons, but is unlikly to take a hit
Seibold - Beats Starmie
Diantha - Can beat Golergheist, and Sucker Punch something if need be.
Additional Comments: Absol is mainly B-Tier because of it's use as a Disk-1 Nuke. Absol rips pretty much everything apart when you get it, due to it's Base 130 Atk, and outspeeding almost everything else at this point. Absol doesn't start to suffer until the very endgame, and even then has use with Sucker Punch. Sadly; the Absolite is post-game. However, if someone trades absolite over, Absol rises to S-Tier. If Absol was stronger latergame, it would probobly be A-Tier.
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On some other topics:
Honedge - I'm thinking A; personally. I never had any issues against them in-game, and it dosen't seem too impressive due to speed issues. Ageisslash is great but comes late.
Charizard - I'd say A because it pretty much has to eat the Megastone, unlike Venusaur, who still crushes everything with or without it. S-Tier is for pokemon that crush almost the entire game without any effort, and Venusaur does that a lot better than Charizard, who you usually have to mega evo to kill things quickly, which adds time with the animation. Movepool issues early/mid don't help either; while Venusaur's movepool is stupid.