Swablu can be encountered on routes 114 and 115 as a relatively common encounter in both. It is also a common encounter when soaring. Additionally, it is obtainable through hordes on both routes, as well as Sky Pillar in the postgame. The Altarianite is obtainable in Lilycove City by showing the collector outside the trainer's fan club an Altaria.
The Swablu line marks its return to its home region with a vastly improved movepool compared to its gen 3 counterpart. However, this is far from the only upgrade the line has seen from the transition to ORAS. Access to an incredibly powerful Mega Evolution has turned this formerly rather average Dragon/Flying type into an extremely powerful and bulky tank with the one of a kind Dragon/Fairy typing.
Tabitha/Shelly (Meteor Falls, tag battle with rival): Swablu does decently against Mightyena if at equal levels, with both Disarming Voice and Snarl being 6HKOs (as an aside Round is a 4HKO). However, Snarl lowers your special attack stat, making this a painful fight. Carvanha will fall over quickly due to its extreme fragility; Numel and the Poison types, however, are too bulky to go down without putting the cotton bird at risk. Particularly Koffing, which carries Self-destruct.
Tabitha/Shelly (Mt. Chimney): See the previous fight for what Swablu can handle, with the Mightyena being absent this time around.
Maxie/Archie (Mt. Chimney): Again, at equal levels, you can attempt to chip damage Mightyena, although Snarl, Swagger and Roar serve as deterents. Golbat is too strong for Swablu to break easily, while Camerupt and Sharpedo destroy it.
Gym #4 - Flannery (Lavaridge Town, Fire-type): No, even Slugma can 2HKO you through Overheat and Rock throw. Meanwhile Swablu is only potentially 2HKOing with Round at best. And the slug could potentially set up Sun for Torkoal, which is never a good thing.
Gym #5 - Norman (Petalburg City, Normal-type): Once more, no. The Slakings will kill you with ease, as will Vigoroth.
Courtney/Matt (Southern Island, tag battle with Steven): This is actually getting sad, let something else fight alongside Steven. Swablu's time to shine is eventually going to happen, but this is not the time.
Tabitha/Shelly (Weather Institute): Once more, Lava Plume/Ice Fang is too much for Swablu to deal with.
Rival (Route 119): Finally something that Swablu can handle. Shroomish, Grovyle, Wailmer and Combusken can be handled with Aerial Ace and care. However, Slugma and Marshtomp have Rock moves, stay away.
Gym #6 - Winona (Fortree City, Flying-type): Skarmory outdamages you at an equal level. Skarmory. Swablu is not helping here. Altaria on the other hand, actually does pretty decently against everything, although the mirror with her own Altaria is risky.
Courtney/Matt (Mt. Pyre): Camerupt is still a pain to deal with through Rock Slide, while Sharpedo is even worse due to Ice Fang being 4x effective on Altaria. If you went and got the Mega Stone first, Mega Altaria stomps on Sharpedo with Return and Camerupt is still somewhat threatening although managable.
Rival (Lilycove City): It is time to unleash the beast. Mega Altaria happily contests Swellow, Return easily 2HKOing at worst while the rival's Aerial Ace is a potential 5HKO even with no defensive investment. Breloom literally cannot hit either form and dies to pixelate Return or STAB Aerial Ace. Blaziken and Sceptile also fall over without much issue to Mega Altaria, with Blaze Kick being feeble and Sceptile literally unable to damage you outside of Slam. Swampert and Magcargo are no-goes for regular Altaria due to Rock Slide (STAB in the latter's case), although Mega Altaria doesn't care and adds them to its list of victims (use Bulldoze for Magcargo).That leaves Wailord, and this sums it up perfectly: 0 SpA Wailord Water Spout (150 BP) vs. 0 HP / 0 SpD Mega Altaria: 26-31 (21.8 - 26%) -- 5.2% chance to 4HKO.
Courtney/Matt (Lilycove Hideout): It's the exact same fight as at Mt. Pyre, only slightly higher leveled. See that fight for how Altaria fares.
Gym #7 - Tate and Liza (Mossdeep City, Psychic-type): With its high mixed bulk and powerful STAB Returns, Mega Altaria makes an ideal choice for being one of the two Pokémon you send after the twins. It can withstand 4 hits from Solrock and 3 from Lunatone while 2HKOing both. Add in the line's resistance to Water and this should be in the bag in no time.
Maxie/Archie (Seafloor Cavern): It's time for revenge. Mightyena is no threat whatsoever to Mega Altaria, getting OHKO'd by Return without doing much in exchange. Return also outdamages Crobat's offensive options if you were on par with Tate and Lisa, so go ahead and take it out as well. Weezing is still a jerk with Sludge Bomb 2HKOing. However, Muk can only 2HKO without a Critical Gunk Shot, allowing you to potentially do the same faster with Earthquake. Speaking of Earthquake, it also 2HKOs Mega Camerupt, which does about a quarter with Rock Slide. Meanwhile Mega Sharpedo is OHKO'd twice over by Return, while its Poison Fang is at best a 2HKO.
Primal Groudon (Cave of Origin, Omega Ruby only): Surprisingly, a fight in which regular Altaria does better than its mega form. Primal Groudon is 2HKOing Mega Altaria with Precipice Blades, while Earthquake or potentially mirror moved Precipice Blades is only 3HKOing at best. In contrast, while regular Altaria takes significantly longer to KO the behemoth, it can only 4HKO Natural cure variants with Lava Plume. Cloud Nine Altaria are on average 5HKO'd in contrast to your Ground move being a 3-4HKO, making this dangerous fight significantly more comfortable to deal with.
Primal Kyogre (Cave of Origin, Alpha Sapphire only): Super effective Ice Beam off base 180 Special Attack. No.
Gym #8 - Wallace (Sootopolis City, Water-type): Set up on Luvdisc. Sweep. Even if it does have Draining Kiss to try and scare you, it is a 7HKO.
Wally (Victory Road): Two options here. You can either set up on his own Altaria and sweep the floor with him or fight him legitimately. In this event, Pixelate Return will still blow away his Altaria, and, due to the AI operating on you being a Dragon/Flying type prior to mega evolving, take no damage from its probable Dragon Pulse. Delcatty is exactly as threatening as you think it is, smack it away. Roselia will require you to dig into your coverage options to avoid the Leech Seed/Toxic combo it packs, however, an unboosted Fire Blast has a high chance at OHKOing. Magneton has Sturdy preventing you for ruining it with Earthquake, although it needs a crit to OHKO with Flash Cannon. Mega Gallade is a beast in its own right, except it needs to use Swords Dance to threaten Mega Altaria with Psycho Cut, while Pixelate Return leaves a crater where it once stood.
Elite Four Sidney (Ever Grande City, Dark-type): Pixelate Returns for everyone.
Elite Four Phoebe (Ever Grande City, Ghost-type): Dusclops is too difficult to set up on due to Curse, however, Mega Altaria can handle it 1v1. The Banettes and Sableye are all OHKO'd by Return. As a final note, Dusknoir can only 3HKO with Ice Punch in response to Mega Altaria's 2HKO Return.
Elite Four Glacia (Ever Grande City, Ice-type): The two Glalie are an easy 2HKO with Return or Fire Blast. However, the main problem here is Hail. Her Froslass duo will happily spam Blizzard under Snow Cloak, which Mega Altaria does not want to deal with. The same applies to Walrein.
Elite Four Drake (Ever Grande City, Dragon-type): Pixelate 2: the reckoning.
Champion Steven (Ever Grande City, Steel-type): You can handle his Fossils with relative ease, and Claydol is not a terrible proposition either. Avoid the Steel types on the risk of death though, especially Mega Metagross, which will effortlessly OHKO Mega Altaria.
Post-Game: With all the Dragon types thrown around in the Delta episode, Mega Altaria's powerful Return will serve you well. Just don't try your luck with Deoxys, Psycho Boost is not pleasant to take without a resist.
At the earliest possible level it can be caught, Swablu will know Astonish, Sing, Fury Attack and Safeguard. At level 11, it learns Disarming Voice, which is a solid addition to its diverse moveset and grants solid coverage, at least in the short term. Level 14 brings Mist, which is not very useful, all things considered. Level 17 brings reliable STAB in the form of Round, shoring up the main weakness Swablu has to endure. Natural Gift, which arrives at level 20, is useless on a Mega evolver due to the berry requirement, although it may have some use if Mega Evolution is banned or restricted in your run. Take Down at level 23 runs off Swablu's weaker attack stat and is outclassed by Return once it evolves, although at level 26, Refresh might be worth your while in a restricted items run. Mirror Move at level 30 is extremely gimmicky, although it may have merit against Primal Groudon. Just before evolving, at level 34, Cotton Guard arrives and allows for Altaria to choose how it wants to function.
Upon evolving, the earliest move avaliable to the line, Dragonbreath, provides a solid way for the line to take advantage of its new typing. Also open immediately after evolving is Sky Attack, through the move relearner. While this is Altaria's strongest STAB option, the charge turn makes it risky. This is also where you can reteach it Dragon Dance, a must for physically focused sets. Dragon Pulse is the line's strongest natural Dragon STAB and a solid upgrade over Dragonbreath at level 40; Perish Song at 46 is a relatively gimmicky option, although it could have uses. At level 52, Moonblast no longer seems like an oddity in its movepool, due to its Mega Evolution, and has a place on special focused Mega Altaria; at level 59 it tries to relearn Sky Attack.
In terms of TMs, the line has a comfortable selection at its disposal. In terms of Offensive coverage, moves such as Aerial Ace, Steel Wing and Incinerate work well in the mid-game in order to round out the coverage of the line, as well as providing Swablu with Flying STAB. Later on, Return is outright devestating on Mega Altaria through Pixelate, while moves such as Earthquake, Fire Blast, Dragon Claw and Ice Beam allow for the line to hit hard in almost any situation. Hyper Beam and Draco Meteor are nuke options on a special set, although the drawbacks to these moves are somewhat unappealing. It also gets Roost, which can help with its longevity in a no items run in combination with Refresh.
Through Dexnav, the line gets access to a cluster of helpful egg moves. These include Agility, which turns Mega Altaria into a fast tank, Dragon Rush, its strongest physical Dragon STAB and Hyper Voice, which is as vital for the special set as Return is for the physical one.
Standard: Dragon Dance, Return, Earthquake, Fire Blast / Dragon Claw
Steel-types: Mega Altaria does not enjoy having to deal with Ice, Steel or Poison-types. Other Fairy-types, although rare, are also not fun for the cotton bird to contest with. Thankfully, Steel-types can withstand all the punishment these types have to offer, and benefit from Mega Altaria's reistances to Fighting, Fire and immunity to Ground-type moves prior to mega evolving.
Water-types: Mega Altaria benefits from the Water-types' resistance to Ice and Steel-type moves. In return, whatever Water-type Pokémon you put alongside the bird, enjoys its resistance to Electric and Grass-type moves.
Psychic-types: With Mega Altaria devouring any Dark or Bug-type that threatens the frequentally frail Psychic type, they find themselves free to tear through the Poison-types that Mega Altaria is unable to handle, even if it has to compete for the mega slot with them.
Ground-types: These freely take on Poison-types threatening Mega Altaria, and their STAB Earthquake is a solid method to dealing with Steel-types as well. In response, Mega Altaria covers their common Water and Grass-type weaknesses.
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.
Swablu Line Ratings
What Nature do I want? This really depends on what you intend for Altaria to do: as a physical attacker, Adamant or Jolly; special attacker prefers Modest or Timid, and bulky likes any defense boosting nature.
Which Ability do I want? Well, once it's mega evolved it doesn't really matter and both are solid if it does not, although Natural Cure has more general utility.
At what point in the game should I be evolved? If caught on Route 114/115, you should probably hit level 35 at or just after Winona. If caught when Soaring, evolve it straight away.
How good is the Swablu line in a Nuzlocke? It's fantastic. While it may have a somewhat rocky start as a Swablu, the moment it evolves you are right on top of getting access to one of the best megas in the game, capable of handling the majority of the late game by itself. Its high and balanced stats, large range of resistances to common types as well as its large movepool make this line one of the best.