Drilbur can be found in dust clouds in Wellspring Cave, Chargestone Cave, Mistralton Cave and Twist Mountain. In Wellspring Cave, its levels vary from 10 to 13. In Chargestone Cave, its levels will be between 24 and 27. In both Mistralton Cave and Twist Mountain, the levels range from 28 to 31. Excadrill can be found in dust clouds in Victory Road, Challenger's Cave and Giant Chasm. In Victory Road, the levels vary from 36 to 37 and 39 to 41. In both Challenger's Cave and Giant Chasm, wild Excadrill's levels range from 47 to 50. In all these locations, Drilbur and Excadrill are a 100% encounter in wild battle dust clouds.
Poor Drilbur never got too much love. It has a bland type, so-so stats, and a horrible learnset in the early game. However, once Drilbur evolves into Excadrill, you got one of the biggest powerhouses in whole Unova in your team. Excadrill's new type is Ground/Steel, which gives it a lot more resistances. That is combined with Excadrill having one of the highest Attack stats in whole Unova, namely a whopping 135. And, as an added bonus, Excadrill's movepool gets a lot better just before its evolution. And the best of it all? If you use Repels, you're guaranteed to catch one of them, as they are a 100% encounter in dust clouds that yield wild Pokémon.
N (Nacrene City): Currently, Drilbur's most powerful moves are Fury Swipes and Metal Claw. It may not even know the latter yet, in which case, don't let it battle. Actually, just keep it away overall. Tympole knows BubbleBeam, which makes it an obvious bad choice. Pidove knows Quick Attack, which might hit harder than you want it to, and Timburr can use a fairly powerful Low Kick. Honestly, there are better Pokémon to check N's at this point.
Gym #2 - Lenora (Nacrene City, Normal-type): Even though you just learned Dig, nope. Both Herdier and Watchog are way too powerful for Drilbur to even consider battling.
Gym #3 - Burgh (Castelia City, Bug-type): Whirlipede is very well possible if you have Dig, but be careful of the combination of its Screech and Pursuit. Then Dwebble comes, which also can't hit Drilbur hard, and gets taken out by Dig. Last up is the Razor Leaf-using Leavanny. Obviously no.
Bianca (Castelia City): Herdier has Intimidate and Take Down, stay away. Dewott, Servine, Panpour and Pansage don't even need explanations. Stay away, take two. Munna can use Psybeam, which might hit harder than you want it to. Try to avoid it. Pignite and Pansear get taken down by Dig.
Cheren (Route 4): Drilbur doesn't like to battle Pidove, because it knows Air Cutter, Quick Attack and Roost. Stay away. Dewott, Servine, Panpour and Pansage are obviously bad matchups. Liepard is a possibility, as it can't really hit hard. And Pignite and Pansear get beaten by Dig.
N (Nimbasa City): Sandile is possible, and will get taken down by Drilbur's Dig. Scraggy is more dangerous, boasting Brick Break. Try to stay away from it. Darumaka gets OHKO'd by Dig. Sigilyph is just too powerful, even if you picked up TM Rock Tomb in Desert Resort. Stay away.
Gym #4 - Elesa (Nimbasa City, Electric-type): The Emolga are annoying. They can use Aerial Ace, which will hit harder than you want it to. Drilbur's Rock Tomb may not do enough damage. Try to use Drilbur only against Zebstrika, which can't really do anything against Drilbur and its Dig.
Cheren (Route 5): Basically the same as the previous Cheren battle. Avoid Tranquill, Dewott, Servine, Panpour and Pansage, and take out Pignite and Pansear, and possibly Liepard as well.
Gym #5 - Clay (Driftveil City, Ground-type): All of Clay's Pokémon will prove to be too powerful for Drilbur. However, if Drilbur has evolved already, then there's another problem, namely the weakness of Steel against Clay's Ground-types. Stay away from Krokorok and Palpitoad for that reason. Clay's Excadrill gets beaten by Dig, but make sure your Excadrill is higher leveled. You do not want his Excadrill to outspeed yours and OHKO it with a lucky crit on Bulldoze.
Bianca (Driftveil City): Having Excadrill makes this battle a lot easier. Herdier still boasts Intimidate and Take Down, but due to Excadrill now being part Steel-type, it won't be able to hit as hard, and Dig takes it out. Pansear and Pignite get beaten the same way. Pansage and Servine can no longer hit Excadrill super effectively, and get beaten by either Return or Dig. Musharna is bulky and can use Hypnosis, but get Dig enough times in, and beat it. Panpour and Dewott should be avoided, although it should be noted that Excadrill's Dig will OHKO Panpour in most occasions. If you don't have Excadrill yet, only battle Pansear and Pignite, as the other are too powerful.
N (Chargestone Cave): Did someone ask for a complete sweep? Boldore can only get 2HKO'd, because of Sturdy, and can be annoying with Mud-Slap. Still easy to beat, though. Ferroseed is bulky, but not bulky enough to take Dig twice. Be wary of its combination of Iron Defense and Iron Barbs, though. Joltik can't do anything, and gets beaten by Dig as well. Then there's Klink...who can't bulk a single Dig.
Gym #6 - Skyla (Mistralton City, Flying-type): Thank the lord for the part Steel-type. Both Swoobat and Unfezant can only hit for not very effective damage. Excadrill's Rock Slide deals with both of them easily. Swanna knows BubbleBeam, stay away.
Cheren (Route 7): With Rock Slide, Unfezant gets taken down. Liepard can't take Earthquake, or if Excadrill hasn't learned that yet, Dig. Earthquake is also powerful enough to OHKO Pignite. Try to avoid Simisear, as it might be able to outspeed you. Dewott and Simipour will prove to be too much for Excadrill. Simisage is dangerous, as it knows Miracle Seed boosted Seed Bomb, and is probably faster than Excadrill. Avoid. Servine, on the other hand, can't take Excadrill's X-Scissor, or if you haven't got it yet, Return. If your Excadrill doesn't know X-Scissor or Return, then leave Servine to another Pokémon.
Gym #7 - Brycen (Icirrus City, Ice-type): Rock Slide deals with both Vanillish and Cryogonal quite easily. However, do not battle Beartic. It will probably not get OHKO'd by Rock Slide, and it knows how to use Brine.
Bianca (Route 8): Bianca's Stoutland and Musharna can't do anything against Excadrill, and get taken down by Earthquake or, in Musharna's case, X-Scissor. Emboar gets OHKO'd by Earthquake, but Simisear should be avoided, as it may outspeed Excadrill and hit it hard with Flame Burst. Samurott and Simipour are, like always, obvious bad choices. Serperior now knows Coil, Leech Seed and Leaf Blade, and can set up Coil against Excadrill's X-Scissor. Another Pokémon is preferred. Simisage may outspeed, and 2HKO Excadrill with Seed Bomb, but only if one of them is a critical hit. Avoid it as well.
Gym #8 - Iris/Drayden (Opelucid City, Dragon-type): Earthquake away against Fraxure and Haxorus, as they both have no moves to even harm Excadrill. Stay away from Druddigon, as it knows Revenge.
Cheren (Route 10): Liepard and Unfezant both fall to Excadrill, the former to either Earthquake or X-Scissor, the latter to Rock Slide. For the others, the same applies as against Bianca. OHKO Emboar with Earthquake, but avoid Simisear, Simipour, Simisage, Samurott and Serperior.
Elite Four Shauntal (Pokémon League, Ghost-type): Cofagrigus is incredibly bulky, and can use Will-O-Wisp as well. Don't even bother. Jellicent can use Surf, Golurk Earthquake. Avoid those two as well. Excadrill outspeeds Chandelure, and OHKOs it with Earthquake.
Elite Four Marshal (Pokémon League, Fighting-type): All of Marshal's Pokémon are pure Fighting-types, that know Fighting-type attacks. Avoid this battle at all costs.
Elite Four Grimsley (Pokémon League, Dark-type): Excadrill doesn't like Scrafty's Brick Break and Krookodile's Earthquake. Avoid them both. Earthquake OHKOs Bisharp. Liepard can't do anything to Excadrill, and gets beaten easily as well.
Elite Four Caitlin (Pokémon League, Psychic-type): Reuniclus is dangerous with Focus Blast, don't battle it. Both Musharna and Gothitelle fall to X-Scissor, although the former is annoying with Reflect. Still, they're no problem. Sigilyph may be possible, but a weakened Excadrill should stay away, as a lucky critical Ice Beam might beat it. If Reflect is up, then don't even consider battling it.
Reshiram/Zekrom (N's Castle): Zekrom gets OHKO'd by Earthquake. Reshiram should too, but could be able to outspeed Excadrill and beat it with Fusion Flare. Don't risk it.
N (N's Castle): Zekrom gets beaten by Earthquake, Reshiram is still dangerous, as it will probably outspeed Excadrill. Beat the former, avoid the latter. Stay away from Carracosta, as it knows Water-type moves and can't be OHKO'd thanks to Sturdy. Take Archeops out with Rock Slide. Defeat Klinklang with Earthquake. Be careful, as Zoroark may come out disguised as Klinklang. It knows Focus Blast and Flamethrower, which could both knock Excadrill out. Rock Slide should deal with Vanilluxe rather easily, but watch out for critical Blizzards, that could beat Excadrill.
Ghetsis (N's Castle): This Cofagrigus knows Toxic instead of Will-O-Wisp. Excadrill is partly Steel-type, and therefore immune to Toxic, making Cofagrigus an easy matchup, unlike Shauntal's. Bisharp gets OHKO'd by Earthquake. Avoid all other Pokémon. Bouffalant knows Earthquake, Seismitoad Muddy Water, Eelektross Flamethrower and Hydreigon Surf, Fire Blast and Focus Blast. Plus, Excadrill has no way of OHKO'ing any of them, except through critical hits.
Post-Game: Excadrill is still as useful as before. Just watch out to not pit it against Water-, Fighting- or Ground-types, and you should be fine.
A level 10 Drilbur comes with Scratch, Mud Sport, Rapid Spin and Mud-Slap, all moves that aren't too useful. Fury Swipes comes at level 12, which still isn't all too useful, but at least better than what it learned up until this point. Level 15 marks the time Drilbur learns Metal Claw. It's probably its best move at that point, and also the only Steel-type move Excadrill can learn in Black and White later on. At level 19 comes Dig, which is finally a great move, and an absolute must on Drilbur. Hone Claws comes at level 22, but Drilbur honestly is too frail to set up on anything. Slash will be learned at level 26, but will be outclassed by Return, whose TM can be bought in Nimbasa City. At level 29, Rock Slide is learned, Drilbur's second great move. An absolute must on both Drilbur and Excadrill. If you evolved Drilbur at level 31, it will learn Horn Drill at 31, and Earthquake at 36. The former isn't a really good move, the latter is one of the best things you could wish for, as Excadrill with Earthquake basically OHKOs almost anything that doesn't resist it at that point. If you chose not to evolve it yet, Drilbur learns Earthquake at 33, but doesn't learn Horn Drill at all. Considering Drilbur's weak stats at that point, though, you should be better off just evolving Excadrill right off the bat. Swords Dance comes at level 42. It could be useful, but Excadrill lacks the speed to be a real sweeper. Sandstorm at level 49 could help with that, if Excadrill has the Ability Sand Rush, but it's not preferred either. Drill Run comes at level 55, but is fully outclassed by Earthquake, which you have for a long time now. And finally, there's Fissure at level 62. Unnecessary and risky.
The first of the useful TMs for Drilbur is Rock Smash, obtained outside of Pinwheel Forest. It isn't stellar, but not a bad move, as Drilbur's movepool is really lacking at that point. Dig comes next, on Route 4, but normally your Drilbur should know that move already. Quickly after, Rock Tomb is available in Desert Resort, a great move for Drilbur at that point. After that, Return can be bought in Nimbasa City, which might be useful for a short time. Bulldoze is the next TM that comes to mind, although Drilbur/Excadrill already knows Dig, and will soon learn Earthquake, which makes Bulldoze mostly unnecessary. X-Scissor will come on Route 7, and is a very useful coverage move for Excadrill, as it can now hit Grass-types super effectively, while they can't anymore, due to Excadrill now being part Steel-type. Soon after, Shadow Claw can be obtained in Celestial Tower, but on most occasions, Earthquake will be more powerful. Aerial Ace can be obtained in Mistralton City after beating Skyla, but isn't really worth a moveslot. Then, after receiving HM Surf from Alder, you can backtrack to Route 6, to pick up Poison Jab, and then go to Mistralton Cave to get Rock Slide. However, the former is mostly outclassed by X-Scissor, and the latter should be already known by Excadrill. Brick Break can be received in Icirrus City, but a super effective Brick Break has the same base power as a normally effective Earthquake, so in most occasions, Brick Break isn't worth the moveslot. The last useful TMs come in the postgame, and are Earthquake, Hone Claws and Swords Dance, all of which moves you should either already know, or moves you don't need.
Recommended moveset: Earthquake, Rock Slide, X-Scissor, Swords Dance
Minimum stats are calculated with 0 EVs, IVs of 0, and a hindering nature, if applicable.
Maximum stats are calculated with 252 EVs, IVs of 31, and a helpful nature, if applicable.
Drilbur Line Ratings
What Nature do I want? Definitely something that boosts Attack or Speed. An Attack boost is usually the best, though. Adamant is the best, but Naughty or Lonely could work as well. Next to those, Jolly, Relaxed and Sassy work as well.
Which Ability do I want? Well...both are only really useful when you're in a sandstorm, and unless you teach Excadrill to use Sandstorm, you'll only be able to use them on Route 4 and in Desert Resort. They're both about equally good...or bad.
At what point in the game should I be evolved? As soon as possible, preferably before Clay. You don't need to wait until Drilbur learns Earthquake at level 33, since its stats are pretty terrible compared to Excadrill's. You'll want that Ground/Steel-type as soon as possible.
How good is the Drilbur line in a Nuzlocke? Incredible. Not only is it a guaranteed catch when using Repels, Excadrill boasts one of the most powerful Attack stats of all Pokémon in Unova. It also has a great type, resisting no less than nine types after evolving, not counting the two immunities it also has. Plus, it learns Earthquake quickly, giving it its most powerful move soon. Its bulk isn't all too great, but it's good enough to take any neutral effective attacks. Two downsides are that it's really weak as a Drilbur, and that it has a nearly useless Ability in-game. However, it is still a great team member to have.