Misdreavus can only be found in Pearl version to those night-owl players, within the Eterna Forest and the Lost Tower. If you're up late at night, and you aren't comfortable with a Gastly on your team, give Misdreavus a look.
After spending two Generations without an evolution, the Sinnoh region gave the Screech Pokemon somewhat new usage with the Dusk Stone-induced evolution, Mismagius. While its stats aren't the greatest, a 105 in Special Attack and Speed means an attack from this Pokemon will hit relatively fast and relatively hard.
Gym #2 - Gardenia (Eterna City, Grass-type): If you decided not to train Misdreavus to level 23, when it learns Psybeam, keep it away from this fight - it won't hit hard enough to do significant damage. If you did level it to 23, your best option is still to keep it out of battle unless you are forced to use it. Psybeam might hit hard enough to cause enough damage to 3HKO anything, and it will do SE damage to Roserade. Just keep an eye on Misdreavus' HP.
Jupiter (Galactic Eterna Building): Nuh-uh. No way. While Zubat isn't the largest threat, you still have to watch out for its Bite. And Skuntank is a big no-no with that Night Slash. If one hit doesn't kill you, the second surely will.
Rival (Hearthome City): Starly is a laughingstock if you're at Level 23, and you should be by this point, and so is Ponyta. Just watch out for Wing Attack and Ember, respectively. Roselia has some threat factor. Even with Misdreavus' moderate Special Defense, you can handle one or two hits, but that's it. The strategy there is to spam Psybeam. The biggest threat is the Buizel, with its high speed and Pursuit attack. Take caution that you aren't caught off guard. As for the starters, it might be better to keep Misdreavus out of the fight. Most of their attacks hit neutrally (with the exception of Monferno's Fury Swipes and Mach Punch, and Grotle's Tackle), and will still cause some pain in Misdreavus' life.
Gym #3 - Maylene (Veilstone City, Fighting-type): Meditite is a safe bet to take down, as the only thing that will even touch Misdreavus here is Confusion. Machoke is a little more dangerous, as it's packing the highly-situational yet highly effective Foresight. You might be able to hurt it, but if it starts off with Foresight, switching out might be the safest bet. Lucario is, by far, the most dangerous part of the fight. Even though he only has one move that can hit, Metal Claw can rack up that Attack stat. Taking advantage of Confuse Ray might not be the worst strategy here, as you can cripple Lucario and use its Metal Claw against him. Be wary of random crits at all times, however, and if you decided to buy Psychic at the Game Corner, make sure you take advantage of that.
Gym #4 - Crasher Wake (Pastoria City, Water-type): For Arceus' sake, keep Misdreavus away from Gyarados. That Bite has the potential to OHKO, and certainly 2HKO. Floatzel is another dangerous bet, as that Pursuit, combined with that speed, can seriously maim Misdreavus before it gets a chance to launch an attack. However, his Quagsire can't even touch Misdreavus, thanks to Levitate and a lack of Water-type moves. Go wild on him.
Rival (Pastoria City): Starly and Ponyta are still laughingstocks (seriously, why hasn't Starly evolved yet?), but keep out for Wing Attack and Ember. Roselia, since the last battle, actually became less dangerous, as Misdreavus isn't affected by Toxic Spikes. Keep on your toes, however, and use Psychic! Buizel might be a little safer to fight against if you have Psychic, but watch out for its attacks. Monferno is a bit easier to take down since the last fight (but take caution of Flame Wheel if you aren't packing Psychic), but keep away from Prinplup and Grotle. Metal Claw will hurt, and Grotle packs Bite now.
Gym #5 - Fantina (Hearthome City, Ghost-type): Unless your Misdreavus is fast, and I mean really fast, keep it away from this Gym. Ghost's mutual weakness against itself is also Misdreavus' greatest hurt. The only fight I would even recommend is against the Drifblim, and that's only if you're packing Shadow Ball.
Rival (Canalave City): Even though Staravia has evolved now, it's still laughably easy to take down with Psychic. Ponyta is still a simple kill if you can avoid Fire Spin. The new threat, however, is that Heracross. Keep away from it and its Night Slash, if you know what's good for you. Roselia continues to reduce in difficulty, just use Psychic. Continue holding caution against the Buizel and its Pursuit. Stay away from Grotle and Prinplup, as their attacks will cause significant damage (particularly Grotle's Bite). However, Monferno is another easy kill, just use Psychic.
Gym #6 - Byron (Canalave City, Steel-type): This ain't Generation 6 with the Steel-type nerf. Misdreavus should avoid fighting Byron. The only thing it can even hit neutrally is the Bronzor, and Hypnosis is still a major threat to avoid.
Saturn (Lake Valor): Kadabra is a simple enough kill. You know Shadow Ball by now, just spam it if it doesn't kill it the first time. But you know what else has Shadow Ball? Bronzor. Keep Misdreavus away from it. If you're confident in your Speed, you can also take on Toxicroak and OHKO with Psychic. Just watch out for Faint Attack.
Mars (Lake Verity): This battle is fairly difficult for a Misdreavus. The Golbat packs Bite, the Bronzor is hard to take down, and Purugly has an immunity to Shadow Ball and knows Faint Attack. Best to let someone else take down Mars.
Gym #7 - Candice (Snowpoint City, Ice-type): Misdreavus' Shadow Ball goes a long way with this Gym. Medicham stands no chance against it, and Snover will go down within 2 hits. Be wary of Abomasnow and its Avalanche, though, as it packs quite a punch when coupled with its low speed. And keep Misdreavus away from that Sneasel! It has very little that can touch it, while Sneasel can easily kill.
Cyrus (Galactic HQ): This Cyrus battle is a breeze as long as you get a Thunderbolt TM from the Game Corner down the street and evolve using the Dusk Stone from the HQ. Murkrow and Golbat should go down within two attacks (but be wary of Golbat's Bite). However, it is recommended to keep away from Sneasel, as you will not have much that will affect it.
Saturn (Galactic HQ): Kadabra is as easy as the prior fight - Shadow Ball FTW. Keep your distance from the Bronzor again, as it still knows Shadow Ball. Toxicroak, as opposed to the previous fight, is a bit easier, however, sacrificing Faint Attack for Swagger. Using Psychic will be a guaranteed OHKO.
Mars and Jupiter (Spear Pillar, tag battle with rival): The Bronzor are somewhat tricky to take down, as Mars' can set up a Light Screen. Still, a couple of Shadow Balls might cause enough to end them. Both Golbat can be simple enough to take down with a simple Thunderbolt or Psychic (but be wary of Mars' Golbat's Bite attack). Keep away from the Purugly and Skuntank, however, as Purugly is immune to Shadow Ball and packs Shadow Claw, and Skuntank resists most of your attacks, and can hit back with Night Slash.
Cyrus (Spear Pillar): The only thing Mismagius should be attacking is the Gyarados, and that's only if you know Thunderbolt. Keep away from Honchkrow's Dark Pulse, Weavile's Night Slash, and Crobat's Bite (if you can't outspeed).
Palkia (Spear Pillar): Mismagius is able to tank most of Palkia's attacks, with the exception of a Critical Spatial Rend. If you aren't using a Master Ball right away, or you're just killing it, spam Shadow Ball to win. Also, if you're fighting Dialga or Giratina, your game is very strange.
Gym #8 - Volkner (Sunyshore City, Electric-type): Raichu should go down to a couple of Shadow Balls, and so should Octillery. However, one should take great caution if using Mismagius against Ambipom, especially if it uses Nasty Plot and Shock Wave. And keep away from Luxray altogether, as that Crunch will cause serious damage.
Rival (Pokémon League): For once, Mismagius should stay away from this fight, as everything holds some serious threat against it. Staraptor can U-Turn into a threat, Heracross packs Night Slash, Snorlax packs Crunch, Roserade uses Shadow Ball, Floatzel uses Crunch, Infernape and Empoleon know Shadow Claw, Torterra uses Crunch, and Rapidash... well, Rapidash is safe to go against, it still doesn't hurt that much. Just watch out if it sets up Sunny Day.
Elite Four Aaron (Pokémon League, Bug-type): For Dustox, Beautifly, and Vespiquen, use Psychic and Thunderbolt, depending on the Pokemon's secondary type. Stay away from Heracross and Drapion, however, as you won't do anything against them.
Elite Four Bertha (Pokémon League, Ground-type): If you decided to use a Heart Scale to reteach Magical Leaf, this fight will be a breeze. Most Pokemon should get OHKOed due to the attack, with, perhaps, the exception of Hippowdon. Just stay aware of Sudowoodo's Sucker Punch and Hippowdon's Crunch.
Elite Four Flint (Pokémon League, Fire-type): First, stay away from Steelix and Lopunny. Steelix resists your attacks, and Lopunny knows Mirror Coat. Drifblim, if you have a good Special Attack, should not be able to withstand more than 3 Shadow Balls, and will probably go down after two. Rapidash should be another simple faint, but watch that it doesn't set up Sunny Day and use Flare Blitz. Infernape is another simple kill, but again, watch out for any sun-boosted Flare Blitz.
Elite Four Lucian (Pokemon League, Psychic-type): Mismagius' time to shine! Effectively, spamming Shadow Ball will be enough to win the fight against 4 of the 5 'mons you will be up against. The only trouble is with Girafarig, who is immune to your Shadow Ball. Have someone else take care of Girafarig.
Champion Cynthia (Pokémon League): Stay away from Spiritomb. Dark Pulse will seriously hurt. Roserade is slightly less dangerous, as you can use Psychic to cause serious damage, but the Shadow Ball it packs will still be painful. Gastrodon is mostly safe to fight, since Magical Leaf should, at worst, 2HKO. Lucario could cause some damage, but you should still be able to handle it if it comes down to it. Stay away from Garchomp, because even though Dragon Rush is the only move it can use to hit Mismagius, it is a guaranteed 2HKO, Garchomp outspeeds, and Shadow Ball is a 4-5HKO after Sitrus Berry. It is recommended to stay away from Milotic, as that Mirror Coat will cause a fatality if you try to attack with Thunderbolt.
Like most stone-induced evolutions, Mismagius does not know any moves through level up other than the level 1 moves it knows, so take caution before evolving! If you catch Misdreavus in Eterna Forest, it will start out with Growl, Psywave, Spite and Astonish. These moves, as you may have guessed, are not very suited for combat, with Psywave's accuracy being unreliable and Astonish being a Physical attack. Misdreavus learns its first actually useful move, Confuse Ray, at Level 14, where you can somewhat turn the tide of battle with a bit of luck. Mean Look is learned at level 19, but is useless unless you run Perish Song (dangerous) or are looking around for a Mesprit. Misdreavus's second useful move is learned at Level 23, Psywave. With a confusion chance and a moderately decent power, it is a good choice until you arrive at the Game Corner TMs. Pain Split, at level 28, is sort of a mixed bag. With a lower-than-average HP stat, as well as one that does not change on evolution, it can provide a bit of safety when weakening a foe with a good HP stat. However, it is not recommended. Payback, learned at level 32, is another unnecessary move, as it is Physical, and Misdreavus and Mismagius have somewhat impressive Speed stats. If you haven't already used the TM, at Level 37, Misdreavus learns its best attack: Shadow Ball. This is almost a necessity for any user of Mismagius. Misdreavus does learn two more attacks at levels 41 and 46 - Perish Song and Grudge - but you won't be using those in a Nuzlocke any time soon.
Misdreavus and Mismagius can learn a fairly decent variety of Special Attacking TMs. From the Game Corner, it is possible to buy Psychic and Thunderbolt. If you don't want to spend the time buying Coins, you can get Shock Wave in Route 215 as a suitable no-miss replacement. If you're willing to sacrifice Accuracy for Power, then Thunder is another replacement, purchasable from Veilstone Department Store. In Victory Road, there's also Dark Pulse, if you aren't running Shadow Ball for some reason. Finally, upon evolution, you can give a Heart Scale to the Move Tutor to reteach Magical Leaf which can take care of some Pokemon that love spamming Double Team.
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.
Misdreavus Line Ratings
What Nature do I want? Attack-reducing Natures are by-and-far the best for a Mismagius. If you had to choose one, though, either Timid (+Speed) or Calm (+SpDef.) would be the optimal choice.
At what point in the game should I be evolved? When you get the Storage Key to enter Veilstone HQ's Basement, there is a Dusk Stone just sitting there. Use it immediately, because by this point, you should know Shadow Ball, whether or not by TM.
How good is the Misdreavus line in a Nuzlocke? The overall rating: Eh. It's a mixed bag. It's movepool is very good, and it can cause some heavy damage to a variety of targets, as well as being a power player during the Lucian battle. However, it will run across a variety of situations that require the assistance of teammates. With this in mind, if you keep Misdreavus safe, it will eventually pay off handsomely with its uses.