I though it was about time that I do this too. :)
B+ Rank
Abra - Here I just quote what Hawkstar said;
"It has two great sets: Sash and SubLO; It's the best Focus Sash user in the tier thanks to Magic Guard preventing hazards from breaking it, meaning that Abra will always live through any single hit.
It can kill any frail sweeper without multi-hit moves regardless of how boosted up their Speed or attacking stats may be. The Sub + Life Orb set will make a kill every time it ends up behind a Substitute, and even without it, can 2HKO basically the whole tier with very few exceptions."
Bunnelby - Without doubt the best wallbreaker in Little Cup, thanks to it's great ability Huge Power, which gives it a scary 28 Attack. Can also hit Ghost-types fairly hard with Thief. It's slow speed and frailness keeps it down, so B+ is fine.
Diglett - A great Pokemon for offensive teams, that can do a lot of things. Set up rocks, Memento and clean out the opponents Fletchling counters is just some of the things this little mole can do.
Ferroseed - Here I quote what Corporal Levi said;
"An absolutely phenomenal supportive movepool allows Ferroseed to really function on teams that require its strengths. It's defensive typing coupled with great defensive stats mean it can take advantage of said movepool extremely well. Although it can be set-up bait to a few Pokemon and is quite prone to being worn down, the utility it brings is considerable."
Omanyte - In my opinion the best Shell Smasher in this metagame right now. After one Shell Smash, it hits a whopping 38 SpA and 26 Speed. Requires a fair amount of support, but damn, it's worth it. Surf/Ice Beam/Earth Power gives it perfect coverage. Only special walls like Porygon can surivive a +2 Surf. Being able to wall Fletch is also really nice.
Onix - Best suicide lead after Dwebble. Hits 17 Speed, and also gets Taunt and Dragon Tail. 55 Attack may not sound too strong, but STAB Rock Blast and STAB Earthquake does more than you think. Can also be used later in the game to stop Fletchling.
Vullaby [Down from A-] - 27 Defense after Eviolite boost is one of the highest in LC, but I feel Vullaby isn't as good as it was. After it loses it's Eviolite, it's pretty easy to take down. It's still a very good Support-mon with Defog and reliable recovering move in Roost, but A- is a bit too high.
Zigzagoon - Give this guy Memento support, remove Ghost-types and Normal-resitsts and it's basically gg. Yes, Ziggy requires much support, but it's the same as for Omanyte; it's so damn worth it. +6 Extremespeed is just so incredibly strong, and it's also +2 priority.
B Rank
Gastly - Gastly looks fairly similiar to Abra when you look at the stats. But while Abra have Magic Guard (which makes it a great Sash-user) and have 19 Speed, Gastly only have 18 Speed and Levitate as ability. But it does have a niche because of STAB Sludge Bomb which is indeed really nice with all the fairies running around, and a strong 100 SpA makes it really strong with Life Orb.
Houndour - Beats Missy with Pursuit and Sucker Punch, and also hits really hard with Life Orb. Problem with Houndour is that's it pretty frail, and it's also weak to Fighting. Life Orb is really the only viable set, since as a bulky Fire-type Pokemon, Growlithe and Ponyta completely outclasses it.
Larvesta - Maybe the best Fighting-type check, but 4x weakness to Stealth Rock really hurts it. It's Bug-typing also makes it very weak against Fletchling. Timburr also loves the 30% chance of burn from Flame Body.
Lickitung - When it comes to wishpassers I prefer Spritzee, but a Spritzee/Snubbull + Lickitung core is really solid. It also have a really good 90/75/75 mixed bulk, and Knock Off, which is really neat.
Munchlax - A long time since I have used Munchlax, but I doubt he have become better since last time. Porygon just outclasses it as a special wall.
Slowpoke - Regenerator and a solid 90/65/40 bulk is cool, but weakness to Knock Off really hurts Slowpokes viability. But if you clean out the opponents Knock Off users, Slowpoke is one of the best walls in Little Cup.
Snubbull - Here again I just quote what Levi said;
"Another Pokemon I've been using extensively as a teammate for Lickitung especially, Snubbull can fit on all kinds of teams that need a good switch-in to Fighting-types. It's quite powerful and has some good coverage options, making it difficult to switch into for offensive Pokemon, and can support the team with Heal Bell or Thunder Wave. It's really a shame that Snubbull doesn't get reliable recovery outside of RestTalk, although such a set isn't actually too bad from my experience."
Vulpix - Vulpix may not look too scary on the outside, but when you take a deeper look, you will quickly find out that this little fox is really powerful. Choice Specs Overheat OHKO's both Timburr and defensive Mienfoo. Heat Rock can also be used for sun teams, for 3 more sun-turns.
B- Rank
Doduo - Doduo is a bit like our old, banned friend Murkrow, just slower, frailer and a worse movepool. But it still have a niche being a good wallbreaker with Life Orb.
Koffing - Was very good during Swirlgar, but Koffing's golden age is over. Things like Abra and Drilbur just totally wrecks it, and there are better Poison-types if you need something for fairies, or to stop Fighting-types with, like Foongus.
Riolu [Up from C-rank] - Set up Swords Dance and spam High Jump Kick. The downside for Riolu is that it does need a ton of support, since Ghost, Fairy and Poison-types all stops Riolu's sweep, and hazards are needed to break Sturdy. It's also fairly frail. But Copycat HJK should never be underestimated.
Torchic - Torchic's viability have got a bit hurt because of the raise of Fletchling usage, but there are also very few Haze/Clear Smog and Whirlwind/Roar users. It have also lost it's best Baton Pass partner, Meditite.
Wynaut - Was fairly popular during KrowTite to lock and KO Meditite, but Wynaut's niche is smaller now after the ban of Meditite. Wynaut is still annoying as always, but there are many ways to play around it.