Note: this contains spoilers, which some people may not like.
Pokemon Black and White have definitely improved the difficulty of Pokemon battles, and going in unprepared is a very bad idea. Especially with your final battle against N and Ghetsis. The legendary dragon N controls and many of the Pokemon on Ghetsis’ team are incredibly strong and can easily destroy an entire team of Pokemon.
However, two ground type Pokemon stand out as being near-essential in helping you win. Excadrill for Black and Krookodile for White are possibly the best Pokemon you can use in the two final battles of the main story.
Excadrill is very useful in Pokemon Black because it has immunity to Zekrom’s strongest attack, Cross Thunder. Excadrill has a very high attack stat and can learn both Earthquake and Drill Run, which will be able to faint Zekrom in only one or two attacks. Because Excadrill can learn both X-scissor and Brick Break, it will also be useful against Ghetsis’ strongest Pokemon, Hydreigon.
Excadrill’s pre-evolution form, Drilbur, can be obtained early in the game so that by the time you face the last two trainers, your Excadrill will be at a very high level. The first place you can find Drilbur is inside the Opening of an Underground Water Vein (English name to be revealed) at about level 10. Drilbur is a little difficult to find because it is only found in dirt clouds, so you may need to walk around in the cave for a while before you have a chance to catch one.
Excadrill’s weakness to Fire-type attacks makes it a bad choice for Pokemon White because N will be controlling Reshiram. Krookodile is a much better choice for this version of the game because it is not weak to Fire-type attacks and has immunity to Reshiram’s Extrasensory attack. Since Krookodile can also learn Earthquake, it can easily defeat Reshiram in a couple of turns. Krookodile can learn a greater variety of attacks compared to Excadrill, including Crunch and Outrage, so it can defeat even more Pokemon than Excadrill. However, Krookodile can not learn X-scissor, so it will have to learn Brick Break or Outrage if you plan to use it against Hydreigon.
Krookodile’s pre-evolved form is Sandile and it can be caught somewhat early in the game in Route 4, so taking a quick excursion to said Route when you reach Castelia City is a good idea. Since many Pokemon trainers are in Route 4 and Castelia City, you can get a good jump-start with training your newly-caught Sandile.
A Sandile with the Moxie ability will be a better choice than one with Intimidate because Moxie will raise Sandile’s attack every time that it knocks out a Pokemon. It’s like getting a free attack boost. If Sandile or any of its evolutions knock out enough Pokemon, their boosted attack stat will make the Pokemon almost unstoppable.
Many people that are into the battling metagame are raving about these two Pokemon, and for good reason. They are probably the best Ground-type Pokemon of the newest generation, and are great assets to any team. If you’re new to the fifth generation, keep these useful Pokemon in mind when you’re planning a team.