Here is a general team threat list I'm gonna compile, big thanks to PenguinX for getting a lot of teams down. A lot of these will simply be restating things he's already said. I will edit in additional archetypes if necessary. Hail balance, sand balance, and rain stall will eventually be on here.
To deal with this team, we need to be able to switch into Genesect U-turn without fearing the switch-in. This is one of the toughest things to do in this metagame, but it shouldn't be too bad with Gliscor. Also, we need a way to control weather because Venusaur will sweep most non-weather teams. Heatran is not dependable because if Venusaur has Earthquake or Nature Power it screws us over. We need a viable way of dealing with Xatu while still being able to control hazards, as this team wins and loses on the hazard war. Choice Band Tyranitar is actually a very good answer to this team as long as it avoids Dugtrio. Some variants have Volcarona, so we need to be able to deal with that.
This is arguably the most solid rain offense archetype in the metagame, so it's pretty obvious why you see it (and variations of it) a lot on the ladder. Politoed is a weather starter you need to prepare for because of its great bulk. Most physical attackers will not stop from doing a little damage with status, be it burn from Scald or poison from Toxic. Controlling weather is super important here because Tornadus-T is free to spam Hurricane if we cannot do so effectively. Latios can spam Life Orb-boosted attacks all day if we can't sponge those or effectively play around it. Dugtrio means that we have to be careful with most of our Pokemon, and Choice Scarf Keldeo is extremely powerful under the rain. To be honest, Gliscor is a free switch-in for a lot of these Pokemon. Scary matchup, we need to cover this at some point. Maybe a specially defensive Rotom-W. Some variants carry Ferrothorn or Thundurus-T, so we need to be able to deal with those.
Sand Offense 1:
We need to be able to deal with a few Pokemon. First off, we need a reliable way of taking down Hippowdon. We can bring in Keldeo, but any smart player will immediately switch to Latias anyways. If we get rid of Latias, Keldeo sweeps much more easily. Choice Band Tyranitar is perfect for that. We also need a Steel-type to take on Dragons usually, but we can't become bait for Magnezone. Mamoswine is troublesome for Gliscor, but we can obviously SubPass out to Keldeo and scare it off (the whole point of the set). So yeah as long as we can deal with the defensive threats on this team we're set. Choice Band Tyranitar helps a lot here. Some variants carry Starmie, Latios, and Garchomp.
Sand Offense 2:
We need to be able to deal effectively with all variants of this team; that means we need to prepare for all possibilities. This includes Choice Band, Choice Scarf, and SubSD Terrakion, specially defensive Rotom-W, Expert Belt, Rock Polish, and Choice Scarf Genesect, Choice Specs, Expert Belt, and Life Orb Latios, and Rock Polish Landorus. Yeah, that's a ton of threats. Rock Polish Landorus is obviously problematic if we cannot control momentum. Choice Band Terrakion is, in my opinion, the biggest threat you can face because of its raw power, and Rotom-W can take on Keldeo fairly well and even burn or paralyze it in the process. The key here is again getting hazards down and playing aggressively. You can't win here with defense; offense, prediction, and aggressiveness are the keys to victory. Some variants carry Starmie, Garchomp, Heatran, and Latias. Choice Band Tyranitar is sometimes a godsend, but it can also be a liability here.
This is always an annoying matchup because of the sheer power of all Dragons. Mamoswine is a tough Pokemon to switch into because of its damage output, and our catch-all physical wall happens to be 4x weak to its main STAB. Haxorus is tough to beat down, and we can't effectively wall it because Magnezone lurks in the midst, ready to take down our counter to Dragons. Latios is extremely powerful, and it hinders our Keldeo sweep, but an effective way to deal with it is obviously Choice Band Tyranitar. This also helps against Starmie and it can generally tank a hit from Dragonite at full health and retaliate with an OHKO. Definitely a strong candidate against these types of teams. Obviously offensive pressure and momentum are key in these situations. Some variants include Salamence, Heatran, and Magneton.
We definitely need a way to control hazards against these types of teams. We can't allow Deoxys-D to set up too many layers, as it can put us in a hole early on in the game and make it hard for us to come back. Additionally it would limit our sweep. Sadly, Tyranitar happens to be a liability in this case, though it does get the KO on Deoxys-D. Dark moves just help Genesect and Terrakion have fun, and Gengar can OHKO (if I recall correctly) with Focus Blast. We definitely need help against these teams, as heavy offense can punch some serious holes against us. Offensive momentum is key, but a way to control hazards and an effective Choice Scarf user are definitely necessary against these teams. That comes later on in building the team, though. Some variants include Rotom-W, Scizor, and Keldeo.
Okay, yeah it's a stupid team archetype, but if you don't prepare sufficiently for Baton Pass, you're going to get swept. Luckily, Gliscor can attempt to get a Substitute up and Baton Pass to a sweeper and boost along with the opponent. Keldeo does well, as Vaporeon can't touch it and it will be the primary switch-in to Keldeo. Once it Baton Passes off to another Pokemon, Keldeo can just hit hard with Hydro Pump or Secret Sword when appropriate. However, this can also fail to work if Vaporeon can boost its Special Defense and pass off to Mew. We just need to play this correctly. Tyranitar does help here a lot, but you can't always depend on it. Some variants include Umbreon, Zapdos, and Celebi.
Anyways I hope we find this list helpful when we're building a team. Keep in mind that you don't want to react to threats, you want to pose a threat. Don't try and make a team that can switch into all of these Pokemon, because that just doesn't work. We'll look back at the team list when we finish up and see how we fare against the rest of the metagame. While I didn't add them, rain stall and sand balance typically work well, but Keldeo can generally sweep both archetypes, so we're set.