Ok I'm posting my thoughts on the pokemon I used. My team was Samurott, Leavanny, Magmortar, Steelix, N's Sigilyph and Zangoose.
I agree with Oshawott's current position in High. It kinda sucks as an Oshawott but take off when it first evolves, becoming a very good water-type. It's pretty much the same as BW1.
Magby in Mid is also fine by me. I hate how late it evolves mostly, although it is pretty good overall.
I used N's Sigilyph which isn't being tiered, although I don't think the extra experience really changes that much about it. It's currently in High which is fine. I think a case for Top COULD be made, but I won't be the one making it!
For Onix, I think it's going to need 2 entries since we aren't assuming trade evolutions: one where you are able to evolve it and one where you aren't. Onix would be terrible without evolution. I put up with it until Chargestone Cave and it was barely useful giving that evolution was inevitable (it shits all over Elesa, for instance) but I can't understand why anyone would want to use it the whole way through!
So yeah, these are submissions for Sewaddle, Onix (evolve into Steelix) and Zangoose. Yes I know I already posted about Zangoose but I wanted to put it in the right format.
Sewaddle: - Mid Tier
Availability: Found on Route 20. It is fairly common and easy to find.
Stats: Leavanny has good stats overall. 103 Attack and 92 Speed make it a strong attacker. Its defences aren’t mind-blowing but 75/80/70 isn’t the worst out there, and it can shrug off a hit or two assuming that its typing isn’t disadvantageous to the situation.
Typing: Grass/Bug is a hit-and-miss STAB combo. Both are resisted by Poison, Fire, Flying and Steel, but the combo covers Water, Rock, Ground, Psychic, Grass and Dark. It should go without saying that Grass/Bug is a poor defensive type as it carries 6 weaknesses (including 4x weaknesses to Flying and Fire attacks). On the other hand, resistances to Water, Electric, Grass, Fighting and Ground are helpful. Overall, you’ll need to pick your fights carefully.
Movepool: Sewaddle has access to good physical STAB attacks. Bug Bite at level 8 is neat and makes Sewaddle surprisingly tough, and just as Bug Bite and Razor Leaf start becoming weak it gets Leaf Blade and X-Scissor. If you wish you can try sweeping with Swords Dance, as long as you don’t do anything stupid like set up against a Flying type. Leavanny’s main problem is that it has absolutely nothing to hit Steel types with, and its coverage options don’t really help much against the 4 types that resist its STABs.
Major Battles: Roxie wall you. Against Burgh you have super-effective Bug Bite for Swadloon and Leavanny. Your Electric resistance is helpful for Elesa but watch for Zebstrika’s Flame Charge. Your Grass STAB is ideal for Clay and Marlon but stay away from Skyla. Leavanny can help against the elite 4, particularly against Caitlin (bar Sigilyph) and Grimsley (watch out for Aerial Ace and Rock Tomb).
Additional Comments: Swadloon evolves into Leavanny by happiness. This isn’t that big of a deal in BW2 and there is a good chance that you’ll have Leavanny by level 21. Having a Pokémon with 103 Attack that early is pretty sweet. Leavanny can be a useful addition to you team as long as you provide it with plenty of team support to account for the shortcomings of its typing.
Onix (evolve into Steelix): - Mid Tier
Availability: Onix is found in the Relic Path, accessible via Castelia Sewers. It’s somewhat rare (5%), although it is more common in ground shaking spots (20%).
Stats: Onix is well known for its bad stat distribution. 160 Defence seems impressive but 35 HP lets it down somewhat. 70 Speed makes it fast for a Rock type, for whatever that’s worth. Unfortunately Onix has a terrible 45 Attack, and it can’t take unresisted special hits for very long with just 35 HP and 45 Special Defence. Thankfully, Onix improves significantly after evolution. It loses a ton of Speed but becomes more durable and can inflict better damage (although 85 Attack is still a bit low).
Typing: Rock/Ground has its ups and downs, although it isn’t great overall. 4x Water and Grass weaknesses are horrible, and Fighting, Ground, Steel and Ice weaknesses on top of that don’t do it any favours. Still, Onix carries some useful resistances (Fire, Flying, Poison and Rock) along with an Electric immunity, which may be helpful for some teams. Upon evolving to Steelix, it becomes Steel/Ground, which is a much better typing. Steelix gains a ton of resistances and sheds a few weaknesses, all in exchange for its Fire resistance (now a weakness). It’s more than a fair trade!
Movepool: The thing that saves Onix from being truly worthless before evolution is its early access to STAB Dig, which partially makes up for its low Attack. It also gets Strength and STAB Rock attacks, providing it with good coverage. Onix and Steelix actually have wide movepools. Beyond STABs, you get Crunch, Double-Edge and the elemental fangs. Strong coverage really helps make up for the middling Attack stats that Onix and Steelix carry.
Major Battles: Ultimately it depends on when you evolve it. It should be said that Onix may well be the best counter to Elesa in the game because it resists all of her attacks besides Emolga’s weak Pursuit, and it has super-effective STABs for her whole team (and Smack Down can even be used to make Emolga vulnerable to Dig). Onix does less well against Burgh (Steelix is an ok choice for Burgh though) and Clay. Onix should be evolved before Skyla and Steelix can beat Swoobat and Skarmory one-on-one. Aside from Flygon, it does well against Drayden too. It should skip Marlon obviously. Its performance against the elite 4 is good. Aside from Marshall, it can contribute in all battles as long as you keep it away from the wrong opponents. If it has Sturdy, it can also be a great counter to Iris’s Focus Sash Dragon Dance Haxorus.
Additional Comments: You have the option of evolving Onix right away (backtrack to Virbank Complex and use Magnet Pull to fish out Magnemites until you get one holding Metal Coat) or waiting until Chargestone Cave. Onix/Steelix can be a good choice either way, so don’t worry if you don’t want to wait around to evolve it as soon as possible. It is a good idea to give Onix Eviolite while it's unevolved to buff up its defences. If you are unable to evolve it into Steelix... you probably shouldn't be using it! Sturdy is probably the better of its abilities. Rock Head is only good if you want to run Double-Edge, and Sturdy is more useful overall.
Zangoose: - Mid Tier
Availability: This is found on Route 7 and has a low encounter rate (5%). It may need a small amount of grinding to catch-up, but thankfully there is a breeder here that can be rebattled that provides HP EVs (meh) and Attack EVs (cool).
Stats: Zangoose’s stat distribution is ideal for an efficient playthrough thanks to an emphasis on Attack and Speed. 115 Attack is very good and 90 Speed is more than adequate in BW2. However, Zangoose has awful 73/60/60 defences and tends to accumulate damage very quickly.
Typing: This is probably the worst thing about Zangoose. Although Normal isn’t a bad typing in itself, it effectively robs Zangoose of any possibility of a super-effective STAB, something it would dearly love to have to ensure more kills. Given how frail it is, Zangoose needs to be able to kill things before it gets hit back, and sometimes a neutral STAB attack isn’t enough. Furthermore, Normal’s complete lack of resistances (bar a Ghost immunity) means that Zangoose will be hoping that its bad defences are enough to survive incoming hits (sometimes they aren't).
Movepool: Normal types are known for their wide movepools and Zangoose is no exception. It gets plenty of STAB options to pick from with Fustration and Return being the best of the bunch. It can complement its STAB with Close Combat and Shadow Claw, which cover all the types that resist Normal. It also gets X-Scissor, Rock Slide, Aerial Ace and the elemental punches, all of which may be useful for particular teams. It has a wide special movepool but has no business using any special moves. Zangoose can use Swords Dance to increase its power although it needs to be careful not to set up in front of something that can kill it straight away.
Major Battles: This comes down to what you give it. Against Skyla you can use Rock Slide, Shadow Claw (Swoobat) or just its STAB to contribute. Ice Punch can be used for Drayden, but Haxorus may survive and set up Dragon Dance, and Druddigon can hit you with Revenge. Thunderpunch is available for Marlon (and Close Combat for Carracosta). As far as the elite 4 goes, Grimsley is the best match-up thanks to Close Combat, but just watch out for Scrafty and Krookodile’s intimidate.
Additional Comments: N/A