Ralts can only be found on Route 102, and has an encounter rate of 4%. A Dawn Stone can be obtained from Wally after defeating him at Victory Road. However these can be accessed significantly earlier through Super Training or as a prize from Psychic Inver for beating him in Mauville City.
As the other option open to male Kirlia, Gallade boasts earlier accessibility and the useful Fighting sub-typing making Poison-types significantly safer to deal with in comparison to Gardevoir. One problem, do not expect to be abusing its mega evolution anytime soon, it's first accessible after you complete the Delta episode.
Gym #1 - Roxanne (Rustboro City, Rock-type): This is not a fight you should risk your Ralts in, as the Pokémon here have strong physical attacks, and your starter, no matter which one you chose, should generally be able to handle the fight better than anything else you could have.
Gym #2 - Brawly (Dewford Town, Fighting-type): Machop should go down easily to a few Confusions, although Seismic Toss may hurt. Makuhita can be taken care of as well, if you still have plenty of health. If you plan to fight Makuhita, don't equip an item; Knock Off will hurt A LOT with a boost, although Ralts' Fairy-type fortunately nullifies its Dark weakness.
Rival (Route 110): If you still have a Ralts, you should really just have it handle Shroomish or Wailmer, as the starters and Slugma will be hitting rather hard. You should really have a Kirlia at this point, though, in which case you can use Magical Leaf to easily deal with Marshtomp and Wailmer, and Confusion should be strong enough for you to take out Combusken, although Flame Charge is still very hurtful. Gallade suffers from being stuck without access to physical moves here, so it might be better to hold off on evolving it for now.
Wally (Mauville City): Your Ralts has evolved and his hasn't, so you naturally have the advantage. Just use one or two Magical Leaf or Disarming Voice and it'll go down. Meanwhile Gallade just smacks it about with its high attack stat.
Gym #3 - Wattson (Mauville City, Electric-type): While Kirlia would struggle to do much here, Gallade goes on a rampage through STAB Low Sweep/Power Up Punch and Bulldoze. Just bring Paralyze heals, Magnemite has Sturdy and Thunder Wave to put a damper on your sweeping.
Tabitha/Shelly (Meteor Falls, tag battle with rival): Gallade decimates everything Team Aqua brings to the table here between STAB fighting move of choice and bulldoze. Team Magma is more of a threat due to Mightyena having intimidate instead of Quick Feet, although that can be undone through Swords Dance. Just be careful with Koffing, Self-Destruct is not fun to deal with, even if it's not as deadly as in gen 4.
Tabitha/Shelly (Mt. Chimney): See the above fight, just without Mightyena.
Maxie/Archie (Mt. Chimney): Mightyena is pretty much the same as the previous one you fought, only Swagger can be annoying if left unchecked. Golbat is a risk due to Gallade not being able to make much in the way of progress without a Psychic move not coming off its miserable special attack stat while Sharpedo implodes to your Fighting move of choice. Camerupt will put up a fight between STAB Lava Plume/Earth Power, although between Bulldoze and liberal usage of healing items, Gallade should come out on top.
Gym #4 - Flannery (Lavaridge Town, Fire-type): Set up Swords Dance on Slugma and then proceed to OHKO everything with Close Combat. If using Low Sweep instead, Gallade needs to use Swords Dance twice in order to ensure the OHKO on Torkoal through Bulldoze. Thankfully, Slugma is not able to have a certain 2HKO with Overheat even if it sets up Sun first.
Gym #5 - Norman (Petalburg, Normal-type): Gallade can take on the first Slaking as Close Combat is a 2HKO unboosted while Retaliate is the same. Truant thankfully makes this doable. However do not attempt to immediately attack with Close Combat if Gallade has more than 85 speed, as the defense drop gives Slaking a high chance to OHKO. If Gallade has less than 71 speed at this point, this is where it's contribution in this fight ends. This number allows it to outpace Norman's Vigoroth and OHKO it with Close Combat before it does the same with Retaliate. The final Slaking is certainly where Gallade abandons the scene, as it's boosted Retaliate is not pleasant for even those who resist Normal to endure, although it can potentially bring it down if switched back in later on a Truant turn. Gallade does need 91 attack to ensure the OHKO on this one however.
Courtney/Matt (Southern Island, tag battle with Steven): Sharpedo implodes to Close Combat. Camerupt might be a pest thanks to its neutrality to Gallade's STABs, but it's pretty much the same as last time, just be careful about letting it raise its defense with Curse and switch out to anything with Surf if it starts get too hot for Gallade to handle. The Poison-types fall to Psycho-cut or failing that, Steven's Metang.
Tabitha/Shelly (Weather Institute): Sharpedo implodes to Close Combat. Camerupt might be a pest thanks to its neutrality to Gallade's STABs, but it's pretty much the same as last time, just be careful about letting it raise its defense with Curse and switch out to anything with Surf if it starts get too hot for Gallade to handle.
Rival (Route 119): Everything dies to Close Combat.
Gym #6 - Winona (Fortree City, Flying-type): Why is Gallade present here?
Rival (Lilycove City): Swellow is a no-go but everything else can be dealt with through Gallade's stellar attack stat and incredible coverage options.
Courtney/Matt (Lilycove Hideout): To risk sounding like a broken record, Sharpedo dies the moment the Close Combat button is pressed, while Camerupt might last a while.
Gym #7 - Tate and Liza (Mossdeep City, Psychic-type): While Gallade's neutrality to Psychic seems unappealing, its high special defense and access to Leaf Blade and Night Slash make it a pretty competent fighter in this hectic confrontation. Plus that special defense means it can endure allied Surfs pretty well to boot.
Maxie/Archie (Seafloor Cavern): Mightyena crumbles under Close Combat and this time it does not even have Swagger to try and annoy you, although Taunt can get in the way of Swords Dance. Not does it matter when Crobat has Acrobatics to force you out. You can freely come back in on their other Poison-type and slice it with Psycho Cut. Now for the megas. Sharpedo is literally the exact same as always, Close Combat OP please nerf and Camerupt now has to contend with Earthquake.
Primal Groudon (Cave of Origin, Omega Ruby only): 0- Atk Primal Groudon Precipice Blades vs. 4 HP / 0 Def Gallade: 120-142 (92.3 - 109.2%) -- 56.3% chance to OHKO. I somehow doubt you went fully defensive with this so don't bother, Close Combat is only a 3HKO anyway.
Primal Kyogre (Cave of Origins, Alpha Sapphire only): 0- SpA Primal Kyogre Origin Pulse vs. 4 HP / 0 SpD Gallade in Heavy Rain: 114-135 (87.6 - 103.8%) -- 25% chance to OHKO. See Primal Groudon for where Gallade should be in this fight, even if there is a possibility that the stars have aligned in order to allow this to occur: 252+ Atk Gallade Leaf Blade vs. 0 HP / 0- Def Primal Kyogre: 140-166 (96.5 - 114.4%) -- 81.3% chance to OHKO.
Gym #8 - Wallace (Sootopolis City, Water-type): Set up on Luvdisc, probably heal off attract with the Red Flute, and then proceed to sweep.
Wally (Victory Road): Altaria ends up on the receiving end of a Stone Edge or two. Just be careful of Cotton Guard and Aerial Ace. Reminder that you should have Ice Beam on something by now. Delcatty does a Sharpedo in response to Close Combat and Roselia withers to Psycho Cut. Magneton is annoying thanks to Sturdy even if it cannot really do that much to Gallade. His Mega Gallade is not worth fighting simply because the mega is Gallade+.
Elite Four Sidney (Ever Grande City, Dark-type): Close Combats for everyone.
Elite Four Phoebe (Ever Grande City, Ghost-type): Night Slash is probably your best friend in this fight. Gallade's high special defense helps in confronting the twin Banettes as well as her ace Dusknoir. Sableye should be avoided regardless due to its neutrality to Night Slash through its typing as well as Foul Play, which is not fun to endure. Meanwhile Dusclops can be handled due to its lackluster offensive presence although Curse is a nuisance. Overall, not terrible but there are better options for this fight.
Elite Four Glacia (Ever Grande City, Ice-type): Close Combat for every.... okay Night Slash the Froslass duo and then Close Combat all the remaining things, just be above level 54 in the event Walrein somehow survives and tries to Sheer Cold Gallade to death.
Elite Four Drake (Ever Grande City, Dragon-type): You can beat Kingdra and the special attack focused Flygon down here, but a Fairy-type or something with Ice Beam are significantly better suited for this fight.
Champion Steven (Ever Grande City, Steel-type): Skarmory uses Gallade as an chance to set up more layers of Spikes than you thought possible, it'd probably poison you as well before Gallade comes close to bringing it down. Claydol can be taken on through Night Slash, although you will probably want to give Gallade Brick Break beforehand if you intend to fight it. This is to deal with its dual screens. Aggron is doable, just break sturdy before trying to crush it with Close Combat or risk death by Earthquake. Cradily is pretty manageable through Close Combat while Armaldo will go down to a few Stone Edges/Rock Slides. Do not engage Mega Metagross with Gallade however, your Pokémon will die.
Post-Game: Gallade does relatively well against the rival in the final battle, but then so does anything due to the level gap. Sadly Gallade sees its usefulness drop off in the Delta episode with all the Dragon, Flying and Psychic-types flinging high power attacks around. Still serves as a pretty good answer to whatever Courtney or Matt have to offer though. Plus if it survives all of that, it finally gets to show off its Mega Evolution against the few remaining challengers.
Ralts starts off with just Growl, but luckily learns Confusion at level 4. It then gets Double Team at level 6 and Teleport at level 9; Teleport is nice in lieu of Fly, so long as you have a spare slot to keep it. The first Fairy STAB available is Disarming Voice, at level 11, which complements Confusion nicely. Lucky Chant at level 14 may be surprisingly useful, removing one of the biggest damage variables in a nuzlocke; again, though, it will find a tough competition for the move slot. Ralts also gets Magical Leaf at level 17, which offers good coverage and has a nice base power. Its last move before evolution is Heal Pulse, learned at level 19, but don't take it. Kirlia has a whole range of moves that would be useful if you were going for Gardevoir, but this is Gallade's page.
Like Gardevoir, Gallade has a large selection of TMs to pick from in order to improve its movepool. Rock Tomb, Low Sweep, Power up Punch, Bulldoze and Aerial Ace all pad out its moveset early on, meaning that Gallade is not forced to rely on special attacks until you reach Fallarbor Town. Later on it gains access to moves such as X-scissor, Rock Slide, Earthquake, Poison Jab and Stone Edge, allowing this super-versatile Pokémon to tailor its moveset for any threat. It also gets a bunch of Special moves which are not of note, giving Gallade's low Special Attack and support moves in the form of Will o Wisp and Thunder wave which allows it to cover its defense or speed respectively.
Unlike Gardevoir, Gallade does get some millage out of its dexnav egg moves, and by that I mean it appreciates priority in the form of Shadow Sneak.
Recommended Moveset: Swords Dance, Close Combat/Brick Break, Psycho Cut, Leaf Blade/Night Slash/X-scissor/Stone Edge/Earthquake/any one of Gallade's many coverage moves.
Physical tanks: Gallade's ability to go on a rampage is somewhat inhibited by faster physical attackers aiming to prey on its somewhat underwhelming defense stat. These Pokémon compensate for this, and benefit from Gallade's high special defense.
Fast Sweepers: Once more, Gallade's questionable base 80 speed means that it looks to its teammates for support in dealing with fast threats. Unlike the walls mentioned prior, these aim to eliminate the threat before it has a chance to attack.
Steel-types: Gallade benefits from having Pokémon present to stand up to the Flying and Fairy-types looking to ruin its parade. Being resistant to Psychic is also a benefit, despite Gallade's serviceable special defense. In exchange, Gallade provides a competent answer to Fire and Fighting-type moves that plague the Steels.
Dark-types: These Pokémon provide an stop to any Ghost-type trying to put Gallade at risk through their strong STAB options and provide an additional safety net to fall back on if a Psychic-type is presenting a problem to Gallade. Gallade handles Fighting-types going after the Dark-types but their shared weakness to Fairy, combined with Gallade's neutrality to Bug-type moves means that they will need the support of a Steel-type to truly shine.
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.
What Nature do I want? Anything that lowers special attack is ideal, particularly Adamant or Jolly. However anything that does not weaken Gallade's attack is suitable. If your Ralts has a Special Attack boosting nature, consider letting it become a Gardevoir.
At what point in the game should I be evolved? You should have a Kirlia for the rival battle on Route 110, and evolve Kirlia the moment you get the Dawn Stone out of Super Training, although hold off until after the Route 110 rival battle.
How good is Gallade in a Nuzlocke? It's solid. Able to stand out from Gardevoir and Medicham due to its incredibly diverse movepool and interesting stat spread making it a powerful utility Pokémon, even if it lacks the sheer destructive power of the aforementioned megas.