Basic Latias + ADV OU Theory

Table Of Contents
1 - Latias's Moveset
 a) Overview
 b) CM + Recover
 c) Recover without CM (i.e. support sets)
 d) CM without Recover (i.e. superlati sets)
 e) EVing Latias
2 - Impact On The Meta
 a) The main Pokemon which are checked by lati are...
 b) Latias is checked by...
 c) Luring and ignoring Latias
3 - Building With Latias

1 - Latias's Moveset
 a) Overview
There's 3 different approaches you can take with Latias:
- CM + Recover
- Recover without CM (i.e. support sets)
- CM without Recover (i.e. superlati sets)

In general, 99% of latias should run Dragon Claw. It's neutral against EVERYTHING that's not Steel-type, plus it's STAB.

 b) CM + Recover
MonoCM is one route - dragon has great neutral coverage. The main move you would consider here is Refresh, so that you can't lose to Toxic Blissey (among MANY benefits). Safeguard and Substitute are inferior to that in most circumstances, as is a RestTalk approach. Roar is an alternative that gives you interesting options against other CMers.

If you opt for coverage, HP Fire and Tbolt are the most interesting options. HP Fire has perfect neutral coverage with Dragon Claw, and hits Steel-types like Rachi, Forry, Skarm, Metagross, etc. It doesn't let it insantly win vs them, but it needs a lot less chip to break through. Thunderbolt and Surf are both generally inferior but still hit Steel-types. Thunderbolt does more to Skarmory and to Suicune. Surf also hits Steel-types neutrally and does more to Tyranitar, but Tyranitar is not that great of a Latias check and you should be focused more on targeting Steel-types in most circumstances.

 c) Recover without CM (i.e. support sets)
Latias has some interesting moves like TWave, Roar, Toxic, Light Screen, Wish, and so on. Something like Recover DClaw TWave Roar is probably playable on the right team.

 d) CM without Recover (i.e. superlati sets)
If you're dropping Recover you really want Lati to be all out attacking. Probably this looks like DClaw + 2/3 of HP Fire/Surf/TBolt to hit steels and tyranitar hard. Something like Sub/Refresh/Roar could be interesting.

 e) EVing Latias
The first thing to consider with Latias is how fast it should be - it has the same base speed as Gengar. Here are a number of benchmarks:
28 - Jolly Breloom
56 - Ada Hera
96 - Modest Molt
160 - Jolly Hera
176 or 68+ - Modest Zap, Mence
208 or 96+ - Timid Molt, tie with SpDef Gengar
176+ - +Spe Mence, Zapdos
184+ - +1 252 DTar
252+ - Max 110 - Opposing Lati, Gengar

Investing in SpAtk and bulk or not is definitely something you'll notice. I have less advice here, but going max SpAtk with Timid is nice and makes Lati strong enough that TTar is pretty easy to overwhelm with spikes support. Investing in bulk will help with checking Breloom and electrics like Zapdos and Jolteon.

2 - Impact On The Meta
 a) The main Pokemon which are checked by lati are:
  - Electrics like Zapdos and Jolteon
  - Waters like Suicune, Starmie, and Swampert
  - Celebi
  - Gengar
  - Moltres
  - Breloom
  - Flygon

It does reduce but not completely blunt the potency of these threats, and the fact it is Spikes immune and extremely difficult to trap* does nerf those Pokemon, particularly in tandem with Spikes.

* You can try trapping Lati with Pursuit Tar, but it won't work unless Latias is severely weakened to begin with - otherwise it can hope to Calm Mind right in front of it's face. Umbreon could hope to trap non Refresh/Roar variants of Latias, but Pursuit won't do much. The ability to withstand hits and land a Toxic is welcome though.

 b) Latias is checked by:
  - Special walls
  - Steel types
  - TTar

Snorlax is reliable against any Latias set, insofar as Snorlax is a reliable special wall, thanks to its high power output alongside its bulk. The extent to which Blissey checks Latias varies greatly with the set, though a set with Toxic + Snatch can reliably beat any Latias set. Refresh sets are otherwise very frustrating for Blissey, but it is excellent against all other variatns. Regice is not very effective against Latias and may have to blow up on it.

Jirachi is a spectacular Latias check, though the effectiveness can vary to a degree based on the sets. For example, Body Slam Wish Jirachi is excellent against any set, but SubCM or CM+Wish will have a harder time against CM+Roar Latias, and Toxic + Fire Punch can do little but sit against the Refresh set. On the whole, though, Jirachi is an extremely reliable answer to Latias. Metagross is a great check too, though HP Fire variants of Latias can put more pressure on Metagross. Skarmory and Forretress can't be relied upon solely to check Latias, due to the presence of Magneton in the tier, but aren't bad checks. Skarmory is excellent against CMRoar Latias, but does little more than soft check other variants. Forretress can do more damage to Latias with HP Bug, but is annihilated by HP Fire.

Tyranitar is a soft check to Latias, and given its incredibly high usage you're likely to use it to check Latias in practice occasionally. Physically inclined tyranitars are better at checking Latias than pursuit tar is, as Modest Crunch doesn't 2HKO +1 0/0 Latias, while physically inclined tyranitar can 2HKO with Rock Slide or HP Bug. +1 252 SpA Latias Dragon Claw 2HKOs 4/0 Tyranitar, and with a layer of Spikes has a good chance to 2HKO Max HP TTar with Leftovers.

 c) Luring and ignoring Latias

A number of Pokemon can lure or ignore Latias.

Most Pokemon on physical offense still function as well or better with latias in the tier. DDTar, Aero, and AgiliGross eat up Latias for breakfast, as does Heracross. DD Gyarados and DDMence aren't inhibited very much either, with Dragon Claw failing to OHKO typical bulky DDMence, and Gyarados only fearing Thunderbolt.

As far as lures go, Claydol and Cloyster can lure Latias with Explosion, while Breloom can lure it with Spore and Stun Spore, and Venusaur can sleep it with Sleep Powder.

CM Spam and specially inclined Spikes teams struggle the most with opposing latias - but at the same time are precisely the kinds of teams that Latias fit well on, so it is a case of giving with one hand and taking with another.

3 - Building With Latias
Latias, as with many pokemon, works completely fine alongside big 5 TSS (with TTar/Skarm/Bliss/Pert/Gar). Spikes work very well alongside Latias, as almost all of its answers are grounded - the main exception being Skarmory, which can be dealt with in a variety of ways.

Conceptually, trappers make for good parterns. Dugtrio can trap Steel-types, though not with ease. It cannot switch into Metagross, and switching into Jirachi is risky, and it can't OHKO most Jirachi variants. It can also trap Tyranitar and Blissey, though trapping Tyranitar is not that valuable and trapping Blissey can be fraught. Magneton can trap Skarmory and Forretress, and occasionally Metagross, but Latias is still on its own when it comes to dealing with Jirachi.

Calm Mind spam is another option for Latias, albeit Latias itself is a problem for some Calm Mind abusers like Suicune and Celebi.