When you're ready to continue your quest, head back to Mistralton City and through Route 7 to Twist Mountain. When you come out into the area with the bulldozers and the house, make sure you check out the cave entrance in the lower southwest corner for TM91 Flash Cannon and take note of the icy rock that will help you evolve an Eevee into a Glaceon should you ever desire.
Icirrus City may be on the small side, but there's plenty of little tidbits to check out here. The "quiz show" house is directly east of the Icirrus Gym, and you can stop by daily to answer a question and get a prize. Also, don't miss the man in the Pokemon Center near the front desk that will buy your rare ores and such for double what you'd normally get.
Wild Pokemon appear in the puddles around Icirrus City, and except during Winter when everything is frozen, just walking across a puddle can initiate a battle.
Can you believe that you can challenge the gym leader right away this time, without having to dispatch any Team Plasma goons or anything? Yup, it's true – and after defeating Gym leader Brycen you'll earn the Freeze Badge and TM79 Frost Breath. Afterwards, Team Plasma will summon you north to Dragonspiral Tower. Head directly north past the gym when you're ready and Cedric Juniper will warn you about Team Plasma and give you an Old Gateau.
Not much to discuss here, but there are lots of Team Plasma battles and items to be had within Dragonspiral Tower. After the scene at the top, Alden asks you to backtrack to Relic Castle, in the Desert Resort area off Route 4.
Wild Pokemon (~level 19-37):
Sandile, Yamask, Krokorok, Cofagrigus
You're now free to go west across the sand pits (slowly!) and down the stairs to proceed further into Relic Castle. As you descend into its depths, it's a bit hard to keep straight which sand pits lead where, but continue down, following the trail of Team Plasma grunts. Ghetsis gives another speech at the bottom, then you, Cheren and Alder head back up to the surface. Professor Juniper calls to summon you to the Nacrene Museum, and once you get there the gym leaders bestow you with the Light Stone.
When you fly back to Icirrus City after receiving the Light Stone, you have two options. You can hurry directly east across Route 8 to the Tubeline Bridge and Opelucid City, or you can hug the northern edge of Route 8 and explore the Moor of Icirrus. There's nothing too exciting there right now, except for a few trainers to battle and common items to find. It has the same wild Pokemon as the rest of Route 8, so unless you want to grind for a bit it's entirely skippable at this point.
Right as you make to enter the bridge, Bianca stops you to battle. Keep going toward Route 9, but make sure to pick up TM43 Flame Charge from the girl on your way.
Wild Pokemon (~level 31-34 normal grass, 36-39 doubles grass):
Normal/doubles grass: Garbodor, Pawniard, Minccino, Liepard
Black only: Gothorita (normal/doubles grass), Gothitelle (shaking patches, rare)
White only: Duosion (normal/doubles grass), Reuniclus (shaking patches, rare)
Shaking patches: Audino (common), Cinccino (rare)
Despite how short it is, Route 9 has more going on that most routes, with tons of trainers to battle and a huge department store called Shopping Mall Nine. The Biker and Roughneck trainers are cool, right? Note the Krookodile embroidered on the back of the Roughnecks' jackets.
Home of the Dragon-type gym, Opelucid City looks totally different depending on which version of the game you're playing. Black's Opelucid is futuristic and sleek, and White's is natural and rustic. After the scene, you're free to explore or challenge the gym anytime. Go get that Legend Badge!
Upon departing the gym, Professor Juniper stops by to give you the Master Ball.
As you pass through the gate north to Route 10, the woman manning the info desk stops you to tell
you about a storm brewing on Route 7. What could it mean? Another, legendary to capture, that's what. Fly back to Mistralton City if you want to capture the legendary Tornadus (Black) or Thundurus (White).
Optional detour: Route 7 and Tornadus/Thundurus
Once you get to Mistralton, head north onto Route 7. Whoa! That lady wasn't kidding when she said it was storming. The effects are really cool here – take a moment to soak it up. When you're ready, head to the house east of Dragonspiral Tower (the healing house) and the old woman will come out to talk to you as you approach. She'll invite you in and tell you about the legendary, and when you leave the house, it will appear and then fly away.
Ah, roaming legendaries are a pain, aren't they? The easiest way to encounter Tornadus/Thundurus is to find a spot where you can go back and forth between the border of one Route and the next area, and continue going back and forth until you enter the Route and it's storming. The spot between Route 6 and Chargestone Cave is a good one, for example.
Before you start though, make sure the Pokemon leading your party either knows the move Mean Look (Watchog and Cofagrigus both learn it via level up) or has the ability Shadow Tag, otherwise chances are your target will flee before you can catch it. Roaming Pokemon are always a good candidate for using your Master Ball, too.
Wild Pokemon (~level 33-36 normal grass, 38-41 doubles grass):
Normal/doubles grass: Herdier, Bouffalant, Foongus (normal grass), Amoonguss (doubles grass)
Black only: Vullaby, Sawk
White only: Rufflet, Throh
Shaking patches: Audino, Emolga, Stoutland, Throh (Black only), Sawk (White only)
You're so close! Head through the grandiose badge check gates and proceed to Victory Road.
If you've played a Pokemon game before, you're familiar with the final haul to the Elite Four that is Victory Road. It's designed to test the strength and endurance of your Pokemon, as well as test your resolve as a trainer.
The best way to get through an area like Victory Road is to make a note every time you reach a branching path, and cross each one off whenever you reach a dead end to make sure you've explored the whole area eventually. Here's a brief guide for getting through it if you get stuck:
In the first area, you can surf across the water to find some items, but eventually you'll want to head back and go up the stairs to the next level. Head south, and outside you'll see a scene that shows you that you can drop off the ledges where there's no railing. Slide down the cliff to the east.
Go back inside the cave and head up the steps to the west, and the go north up more steps. From there, go outside. The eastern break in the railing will send you on a loop that contains TM12 Taunt. You can also go through the eastern door for another loop with more trainers and items. When you're ready to proceed, head through the western-most door on the level with three doors.
Head up the stairs and you'll fight a doctor that will heal you from now on whenever you talk to him. Head up the stairs and then go north. Heading west nets you some more items, and east leads you back outside. Jump down the eastern-most cliff to proceed. Head along the path up the steps until you reach an area where you can either go outside to the south or downstairs to the west. If you've already encountered Cobalion, you can head down those stairs to the west and find Terrakion waiting to be captured. When you're done, go back and head outside.
You have two options here - you can jump down the ledge by the ranger and net some really useful items, including two TMs (TM02 Dragon Claw and TM93 Wild Charge), but that requires some major backtracking. If you're feeling fatigued, you can head straight into the Pokemon League to heal and regroup.
Elite Four and N's Castle
From here on out, you're on your own as you face the final challenge the main quest has to offer. You'll know soon enough if your Pokemon need to go back and level up. You'll have a chance to heal and warp away to finish any unfinished business between the Elite Four and the final showdown in N's Castle, so don't worry if you barely scrape through the Elite Four. If you want to use Reshiram/Zekrom in the final battle, leave a space in your party and the Pokemon will join you after you capture it.
Part one - Nuvema Town, Route 1, Accumula Town, Route 2, Striation City (Tri Badge), Dreamyard
Part two - Nacrene City (Basic Badge), Pinwheel Forest, Castelia City (Insect Badge), Route 4, Desert Resort, Nimbasa City (Jolt Badge), Route 5, Driftveil City (Quake Badge), Cold Storage, Route 6, Chargestone Cave
Part three - Mistralton City (Jet Badge), Celestial Tower, Route 7, Legendaries: Cobalion and Virizion, Route 17, 18 and P2 Lab
Part four - Twist Mountain, Icirrus City (Freeze Badge), Dragonspiral Tower, Relic Castle, Route 8, Tubeline Bridge, Route 9, Opelucid City (Legend Badge), Legendaries: Tornadus/Thundurus, Route 10, Victory Road, Pokemon League
[This guide is still receiving updates. Last update Mar 7, 2011]