[OVERVIEW]
Altaria is an unique Pokémon [Spell it without the accent] in NU, as it is the only fully-evolved Dragon-type in the tier.
It has a decent defensive typing which makes it a solid answer to powerful threats like Magmortar, Combusken, and SD [Write out Swords Dance] Samurott. The offensive Choice Specs set serves It can serve as a pivot on offensive teams with a Choice Specs set, while being threatening with a and its strong Draco Meteor at the same time [This sentence is a bit unclear as it stands; these edits say the same thing in less words.]. Defensive sets can take on a lot of powerful threats in the tier like Sawk [Sawk is banned, so no need to mention it. Some other offensive threat instead?], Pyroar and Combusken easily because of it has reliable recovery in Roost, as well as its and the ability to come in on status users like Weezing, Vileplume, and or Rotom. [I've thought about this sentence for a while and still feel ambivalent about it. On one hand, I'd really like to see the two lists condensed into one for easier readability. On the other, I like the original form's organization. Maybe you should add the word "offensive" between "powerful" and "threats", or change the wording to "take on a variety of threats" to add clarity.]
Altaria faces competition from Sliggoo, which has no SR weakness, a wider offensive movepool, and a more reliable ability. Altaria's defensive capabilities is are hindered a lot by it's [Remove apostrophe] weakness to Stealth Rock and it's [Remove apostrophe] 4x weakness to Ice-type attacks, both of which are very common in the NU meta as most Grass or Water-types run an Ice-type attack for coverage. [It doesn't really make sense to say "both of which" and then only talk about one of the two. You should probably cut the last part of this sentence, but adding a bit about Stealth Rock could also work.]
[SET]
name: Offensive
move 1: Draco Meteor
move 2: Fire Blast
move 3: Dragon Pulse
move 4: Rest / Sleep Talk
item: Choice Specs
ability: Natural Cure
nature: Modest
evs: 252 SpA / 4 SpD / 252 Spe
[SET COMMENTS]
Moves
========
Draco Meteor is Altaria's most spammable move. Fire Blast nails Steel-types such as Steelix, Ferroseed and Klinklang that try to come in on a resisted Draco Meteor. Dragon Pulse is used in situations in which you can't afford to have your Sp. Atk stat lowered by Draco Meteor, but still want to use a Dragon-move. Rest takes advantage of Natural Cure, as your sleep will be cured right away after Altaria switches out. Sleep Talk can be picked used [Personal preference, really, but I think this verb makes more intuitive sense.] over Rest to make Altaria function [This idea isn't implied strongly enough in the original text, in my opinion.] as a sleep absorber, [Change the comma to a semicolon; these are two independent clauses that are closely related.] however, [Add comma] Natural Cure clashes with this as because [It's also possible to add a comma and keep "as," but I prefer not using commas soon after each other like that in my own writing. Anyways, this is clearer than the original.] it removes your the ["You" should only refer to the player, per the Spelling and Grammar standards.] sleep after Altaria switches out.
Set Details
========
Max Speed and Max Special Attack, [Remove comma] together with a Modest Nature make the best of Altaria's offensive stats. Natural Cure is useful as because Altaria doesn't need to worry about a status ailments [Remove "a," pluralize "ailment"] too much, making it easy [The truthfulness of this word varies; some Scalds hurt more than others. I'm not sure what wording would be better, though.] to switch in to things like Scald or Will-O-Wisp for example, and is also used to get rid of sleep, [Remove comma] caused by Rest [the "things like" edit makes the sentence flow better. This sentence should probably be split into two due to its length, in all honesty, because it's a bit meandering even with my edits.].
Usage Tips
========
Altaria is mainly used as an offensive switch-in to status-users [Change hyphen to a space] like Weezing, Vileplume, and Gourgeist, while also being able to check offensive threats like SD [Write it out] Samurott, Combusken and Magmortar due to its ability and typing, respectively. [Remember the sentence I was equivocating over in the overview? This sentence expresses those thoughts nicely, for what it's worth. The edits are for wiping the last frost off the window, so to speak.] Draco Meteor is the move of choice most of the time, as it hits pretty much everything that doesn't resist it for good damage. [Well, Draco Meteor technically hits everything that isn't a Fairy-type. This modifier makes the meaning of the sentence clearer.] Use Fire Blast when predicting a possible switch-in you predict the opponent will switch [The edited version is clearer, and in a better voice.] to something that resists Draco Meteor like Steelix, Ferroseed or Klinklang. In a Situation [Shouldn't be capitalized] where Altaria is on the field, faced off [Too many words here in the original] with a hard-counter like M-Audino [Write out Mega Audino], it is in your best interest to switch out and preserve Altaria, as Fire Blast has quite underwhelming damage output on a neutral hit [The usage of "as" here is better than it was above.]. While Draco Meteor is your most spammable moves, always be wary of set-up pokémon that can set up on a -2 Sp. Atk Altaria, like Samurott, Barbaracle or Jynx.
Team Options
=========
Offensive Pokémon that hate dealing with fast Fire- or Fighting-types like Shiftry, Special [Shouldn't be capitalized] Skuntank, and [include the Oxford comma along with the "and"] or Hariyama are good partners for offensive Altaria as because they help can break eachothers each other's checks and counters. Defog support is really benificial beneficial [Spelling] for Altaria, [Add a comma to make this work] as Stealth Rocks hinder hinders [Stealth Rock, singular, and the accompanying verb change] its ability to take on Mixed [Shouldn't be capitalized] Shiftry, Pyroar and Sawk. [See the comment in the overview about Sawk] Sweepers that need their counters to be severely weakened in order to sweep and hate dealing with status-users, such as Swellow and Archeops, (Swellow, Sawk, Archeops) [You don't really need parentheses here, especially if you're not using them for a similar list just before.] are good partners for Altaria, as Natural Cure allows Altaria to come in on most Status-users [Don't capitalize "status" and remove the hyphen.] and threaten them out with a strong attack [Although I understand the meaning of the sentence, it probably isn't especially clear why Natural Cure allows this. Consider adding a bit of clarification.]. Also, Pokémon [No accent] that deal with Mega Audino, being like Garbodor, Skuntank, Steelix, [Add comma] make for good team members, as M-Audino [Write it out] completely shuts down Altaria.
[STRATEGY COMMENTS]
Other Options
===========
A set consisting of Dragon Dance, Outrage, Earthquake and Roost can be used as a late-game sweeper, however it is easily walled and still weak, even after multiple Dragon Dance boosts. Heal Bell is another option over Earthquake to get past Pokémon [No accent] that use status-moves [Remove hyphen] in order to deal with the set, however it is but that leaves Altaria [Edit for clarity] hard-walled by all Fairy-types and pretty much almost [Edit for professionalism] all Steel-types.
While almost completely outclassed by Sliggoo, a Defensive [Don't capitalize] Altaria set with an EV spread of 248 HP / 148 Def / 112 SpD with and Roost, Heal Bell, Dragon Pulse, [Oxford comma] and Toxic/Haze [I'd change the slash to "or," personally.] can be used as a defensive pivot on Semistall-teams [Don't capitalize playstyles, and remove the hyphen].
Life Orb is an option on the Offensive [Don't capitalize] set, as it [Vague pronoun] can allows Altaria to use Roost instead of Rest, and also switch up between moves [These edits fix the vagueness from earlier.]. The power that Choice Specs gives however, combined with not taking losing 10% of its HP after every attack, makes it [Vague pronoun] the better option. Swapping out Dragon Pulse for Power Swap can be an option to catch opponents off-guard. , since [The following sentence is pretty short and closely related to the previous one; blending the two together like this could work nicely.] Power Swap restores Altaria's SpAtk [Write it out] to neutral after using Draco Meteor. This allows Altaria to get past Specially Defensive [Don't capitalize] Pokémon [No accent] like Mantine better, but doesn't work that often, making meaning that it is [For clarity] not the most viable option. Cloud Nine can be chosen as an ability over Natural Cure to better check sun- and rain-teams [No hyphens necessary], however those [I think it works better if you start a new sentence with "Those". The way it's written now is a bit meandering.] are both quite uncommon, however, and the utility that Natural Cure provides is way more useful most of the time.
Checks and Counters
===================
**Fairy-types**: Fairy-types like Mega Audino and Clefairy are both [I'm not sure what "both is referring to here. I'd recommend taking it out.] immune to Altaria's most spammable move in Draco Meteor and can pass off Wishes or set-up Calm Minds on it. [Neither "off" nor the hyphen is necessary.]
**Ice-types**: Altaria's 4x weakness to ice leaves it vulnerable to any Ice-type move and or Pokémon [No accent. Also, "or" just works better.]. Bulkier [Than what? Consider changing it to "bulky".] Ice-types (Lapras, Piloswine) like Lapras and Piloswine can switch in on Altaria's attacks and easily OHKO it with Ice-STAB-moves their STAB Ice moves, while frailer Ice-types like Jynx or and Aurorus can't safely switch in, but are still able to OHKO Altaria at from full health. [Again, parentheses aren't really necessary, especially when you aren't using them for a similar list later in the same sentence. At the end of the sentence, "from" might work better to convey the point.]
**Steel-types**: Steel-types stop Altaria from spamming Draco Meteor, but should still [Unnecessary] be aware of the possibility risk of Fire Blast [I think "risk" conveys your meaning better than "possibility," but feel free to ignore this suggestion if you're sure that's the word you want.].
**Stealth Rock**: Altaria's role as a pivot or wall is severely hindered a lot [For professionalism] by Stealth Rock, as it is unable to check the things that it's supposed to check when Stealth Rocks are on the field.