Just finished a dog run of X (Furfrou, Houndour, Snubbull, Mightyena), here are my thoughts:
Furfrou is already tiered, but I wouldn't be opposed to B, although the intimidate support I gave it might have been a little much. He just became super bulky with it that I'm probably biased.
Houndour (X): C-Tier
Availability: Route 10 in X only. Potentially before the second gym, although I wouldn't recommend him there.
Stats: 75/90/50/110/80/95, High Special Attack and Speed with usable attack and special bulk, although very frail physically. Evolves early, so stats are nice for that point in the game.
Movepool: Pretty dang shallow for a while. Relies entirely on physical moves by level up, the best special moves are all gotten pretty late via TM. He starts with Bite, which is pretty good for him, and gets Beat Up, which can be surprisingly effective with the right team, and Fire Fang pretty quickly. He only really gets Dark STABs after (Foul Play is nice if situational). He gets Fire Blast and Dark Pulse via TM for STAB, Sludge Bomb is also nice for Fairies. Nasty Plot is available either very late or by move relearner, and he can add in Thunder Fang through Heart Scale as well.
Major Battles:
Grant: No.
Korrina: No.
Ramos: Should have Fire Fang, destroys him.
Clemont: Not great, can potentially beat Magneton.
Valerie: Doesn't have Sludge Bomb yet, but can Fire Fang the Mawile and abuse Mr. Mime's weak defense.
Olympia: Great here, but must watch out for Slowking.
Wulfric: Great again, can sweep easily if you kept Fire Fang for Cryo (maybe even if you didn't)
Team Flare: Doesn't like Scraggy family and some Croagunk, and does pretty badly vs Lysandre, Pyroar being the closest thing to a good matchup.
Rivals: Get's Chesnaught if he's used and Meowstic. Can outspeed Absol if needed. Flash Fire also helps against Flareon.
Elite 4: Does alright vs Malva thanks to Flash Fire, and destroys Wikstrom minus Probopass.
Diantha: A decent enough answer for Mega Gardevoir, and destroys Gourgeist.
Additional Comments: Mine was -SpAtk nature, which sucked, but the was still only 2HKOing things that would nearly OHKO him back, and didn't have a great level up opportunity until Ramos's gym. The biggest problem I found was that I remember a lot of Black Belts and Battle Girls in the later caves which really stifles his level up opportunities outside of gyms. Maybe my time in caves was disproportionately long, but there's a lot of difficulties with patches of almost tutorial level stuff. His bulk also isn't quite enough to handle the mid-game with neutral physical moves, although Foul Play and Beat Up were surprisingly effective.
Snubbull: C/B Rank
Availability: Exact same spot as Houndour, evolves one level earlier and can actually be used in Grant's gym.
Stats: 90/120/75/60/60/45, high attack with decent physical bulk thanks to intimidate.
Movepool: Surprisingly wide. Gets bulldoze immediately and starts with Headbutt and Bite. Level up later gives it Play Rough at 43 and Crunch 59, even Outrage at 67 if you get that high. Can learn the elemental fangs with a Heart Scale and also gets Brick Break, Stone Edge, Dig, and Earthquake via TM. Fairy/Ground is great coverage in and of itself, and the extra coverage is generally a nice bonus.
Major Battles: Grant: Can Bulldoze if desperate, and can potentially be Granbull here.
Korrina: Can't hit super hard, but takes attacks pretty well.
Ramos: I let him take the back seat, but he's not at a huge disadvantage against anything but Weepinbell.
Clemont: Not great but can use Dig if absolutely necessary, has some speed and bulk problems though.
Valerie: Mirror match, and not much coverage help.
Olympia: Can Bite/Crunch here.
Wulfric: Can abuse Brick Break here to beat Cryo and Aboma, might be able to Fire Blast Avalugg as well (I avoided his low SpAtk though)
Flare: Great for everything not Poison-type, and can potentially even get away with some as the Poison STAB wasn't too prevelant from what I remember. Lysandre is alright, can beat Mienshao and Honchkrow easily, Pyroar can be killed if he doesn't kill first, Gyarados has Iron Head (argh) but the Mega can be beaten with some adjustments.
Rival: Can literally kill everything but Delphox with STABs, watch out for faster Special Attackers like Greninja.
Elite 4: Can potentially power through everything here. Play Rough destroys Drasna, Earthquake beats Wikstrom, EQ for Malva with Rock Slide for Talonflame. Siebold is hard, but he can Intimidate Gyarados to negate Dragon Dance, Crunch Starmie, and Earthquake Barbaracle. I don't remember exactly where I used him, but I used him a lot.
Champion: Can beat Hawlucha, Aurorus, Tyrantrum, Gourgeist, and Goodra with something, problems with Gardevoir though.
Additional Comments: Has a lot of good qualities (Fairy-type, early evo, massive attack, Intimidate) but his slowness really hurts it in the long run. He was supposed to be an easy answer to Fighting-types, but they all started running Poison Jab/Iron Head/Steel Wing(Hawlucha), which really sucked. His tiering is really a matter of how much that low speed hurts him, since everything else is pretty good.
Mightyena: E-Rank
Availability: Route 15, which is after Valerie because of Team Flare.
Stats: 70/90/70/60/60/70, pretty mediocre everywhere, has passable attack and bulk thanks to intimidate.
Movepool: Really freaking shallow, Assurance is the best for a while (not really abuseable though), and only gets Dig and Return for coverage. Sucker Punch is nice because of priority, but it's not exactly hitting like a truck. He does get Crunch by Heart Scale I guess (I always forget about those).
Major Battles: Olympia: Quite nice here, although you will need to find a way to level up somewhere.
Wulfric: No real advantages.
Team Flare: Nothing really stands out here, can dig against Electrike, Houndour, Swalot, and Croagunk, although the last one is kinda shaky. Lysandre is mostly bad, since Pyroar outspeeds and uses special attacks and he can't hit anything super effectively other than him.
Elite 4: Can beat Aegislash if you're lucky, and does alright against Chandelure I think. Pretty bad overall though.
Champion: Goureist is it I think.
Additional Comments: Not a lot to say here, he was mostly dead weight for most of the run, and comes pretty dang late. Intimidate was nice, but again, I got shit on by a -Atk nature so he couldn't take advantage of the hits he survived. Not complete F-Tier, but pretty darn close.
Also, I haven't seen any responses to my
Binacle for B-Rank or
Psyduck for D-Rank yet, so read my post (top of page 23, don't have time to link atm) for info.