Tepig as starter: Emboar, Crobat, Excadrill, Haxorus, Jellicent, Gothitelle/Reuniculus,
I just swap Lucky Eggs and Amulet Coins among my Pokemon, so I'm not going to list the items. Before you get the pre-evos of the Pokemon I'm listing, carry around an army of Pickup Lillipups to get you items. Also have a Pokemon that can use Surf before you get Jellicent. The moves are pre-Elite 4, so TMs such as Earthquake are not there.
Emboar
Ability: Blaze
EVs: 252 HP / 252 Atk / 4 Spe
Adamant Nature
- Fire Punch / Flare Blitz
- Low Kick
- Bulldoze
- ThunderPunch
The best of the starters is the worst of the starters. Like any paradox, once you think about that statement, you realize it's truth. Emboar is outclassed completely by the powerful Darmanitan. And having Emboar means you can't have two of the best Pokemon in the game, Volcarona and Lucario, without doubling up on your types, which is something I never enjoy doing for ingame. Because of these facts, Emboar is the worst of the starters. Now, this Emboar can still do some damage. No Speed EVs, as eventually you'll get to the point where the base speed of your opponent outspeeds Emboar's full speed. So the focus is on HP and Attack, with an Adamant nature. Fire Punch you can get from the tutor and is Emboar's most reliable attack. You can use Flare Blitz however if you either don't mind the recoil or have a large supply of healing items. Low Kick becomes useful later on, getting STAB and doing solid damage to heavy foes you face. Bulldoze and Thunderpunch provide coverage, with Bulldoze even slowing down the foe so Emboar can outspeed slower opponents.
Crobat
Ability: Inner Focus
EVs: 132 HP / 252 Atk / 124 Spe
Adamant Nature
- Fly
- Cross Poison
- X-Scissor
- Wing Attack
Your Flying type. You get it pretty early on, in Castelia Sewers. You can easily evolve it into a Golbat, and probably a Crobat after your next level up. Crobat's main job is to Fly you around. With good stats, this is the best Pokemon to do that for Emboar. Cross Poison is STAB. X-Scissor hits Psychic types hard. Wing Attack is a STAB move you can use when you don't want to use Fly, which I find is often. It also has a whopping 35 PP, so you can go quite some time without a Pokemon Center or Doctor before needing to replenish Crobat's PP. With 31 Speed IVs you hit 327 Speed, enough to outrun any Accelegor. It's a good number to aim for, just so Crobat is faster than everything you face. Then we have Attack and bulk.
Excadrill
Ability: Sand Rush
EVs: 28 HP / 252 Atk / 228 Spe
Adamant Nature
- Earthquake
- Iron Head
- Rock Slide
- Strength
The choice of your Ground type is a hard one. There are many good Ground types in BW2. In addition to Excadrill you have Krookodile, Mamoswine, and Golurk as the ones of note. I won't blame you for choosing any of those three instead of Excadrill, as they're all great Pokemon. However, I find that Excadrill's Attack and Speed give it an advantage over the others. Plus, you get it earliest. Drillbur can be found in Relic Passage Dust Clouds. It soon proves itself handy vs Elesa. Earthquake just tears apart everything in the game. Iron Head also hits hard. And Rock Slide takes down Flying types. Strength is a useful HM for ingame. The Speed EVs allow you to outspeed Zebstrika among other things. Then we have full out Attack and some bulk.
Haxorus
Ability: Mold Breaker
EVs: 108 HP / 252 Atk / 148 Spe
Adamant Nature
- Outrage
- Bulldoze
- Dragon Claw
- False Swipe
You thought Excadrill and Emboar hit hard. Haxorus makes them look like Metapod using Tackle. Outrage just pulverizes the opponent. And since this is inmgame, you can switch out once you take down the foe, meaning you don't get trapped in Outrage as easily as in competitive. Bulldoze offers coverage, and is nice along with Mold Breaker, especially in getting past that damn Boldore Sturdy. Since you'll mostly just crush everything using Outrage, Dragon Claw is there to provide more PP to your STAB. False Swipe is for use in catching Pokemon. The EVs give you nice Speed, great Attack, and some bulk.
Jellicent
Ability: Water Absorb
EVs: 252 HP / 252 SpA / 4 Spe
Modest Nature
- Surf
- Shadow Ball
- Ice Beam
- Waterfall
Your Water type. There aren't really many good Water type options. Jellicent is the best one in my opinion. It has great typing with multiple resistances and three immunities with help from Water Absorb. While you get it later in the game, a bit before getting to the 7th Gym Leader, you get it at a nice level 40. So it doesn't hold your team back when you get it. The main purpose of it is to use Surf, the best ingame move ever. Shadow Ball is STAB. Ice Beam is coverage. Waterfall is another HM. EVs give bulk and offense.
Gothitelle
Ability: Frisk
EVs: 252 HP / 252 SpA / 4 Spe
Modest Nature
- Psychic
- Thunderbolt
- Signal Beam
- Thunder Wave
You use this gal for Black 2. You get it around the 4th Gym, which is nice. I prefer Reuniculus, but that isn't an option for some people. Gothitelle is good also. Solid Special Attack and nice bulk. Frisk is cool, showing you what Pokemon to catch because they have items on them. Psychic is STAB. Thunderbolt and Signal Beam are coverage. Thunder Wave helps in catching wild Pokemon. EVs give bulk and power. It is a nice support Pokemon (support as in helping catch and know what to catch) as it has some power behind it.
or
Reuniclus
Ability: Magic Guard
EVs: 252 HP / 252 SpA / 4 SpD
Modest Nature
- Psychic
- Shadow Ball
- Energy Ball
- Thunder Wave
For use with White 2. Easily better than Gothitelle. This thing hits incredibly hard. And it's bulky to boot. Slowest thing on the field, but so worth it. Magic Guard is a great ability also. Psychic is STAB. Shadow and Energy Ball are coverage. Thunder Wave is to help in catching Pokemon. EVs give power and bulk.