Is it just me who can't wait for Defog+Poison Heal Gliscor to become legal with the gen 4 remakes?
Anyway, it is impossible to deny the profound effect that entry hazards have had on the metagame. I am going to do a sort of "brief history" of them because I think it'd be rather fun to type :)
In generation 1, the prospect of entry hazards had not been introduced. While it was most likely speculated by older, more competitive players of Pokemon Red/Blue/Yellow, it was merely something which you could only dream of laying down on the opponent's side of the field. However, in generation 2, the Forretress line was introduced for what I suspect was for the sole purpose of showing off the new move Spikes - a move which can be placed on the opponent's side of the field to deal a set amount of damage to grounded Pokemon on switch in - with said pokemon not only having the ability to lay its own spikes, but also to remove them from its own side. While it was never quite on the same level as other spikes and Rapid Spin users for each individual role, it still saw use on some teams due to being the only pokemon with access to both. GSC OU was a very bulky, long-winded metagame due to the fact that everything ran rest, toxic got reset to regular poison when a toxic'd pokemon was switched out and Leech Seed was significantly worse than it is now. This gave Spikes a very solid niche in being the most reliable way of dealing chip damage to your opponent, with it working like a typeless Stealth Rock which didn't hit Flying-types. Therefore, matches would often come down to the one who was able to control Spikes the best; if you could remove the hazards and the setter, you stood a far better chance than someone who couldn't.
However, the move received a change in generation 3 which can be debated as both a buff and a nerf: it could now be layed up to three times, with 1 layer dealing 6.25% (half of its previous output for 1 turn of laying), 2 layers dealing 12.5% and 3 layers dealing a whopping 25% to your opponent. This meant that controlling them was far more important than in generation 2, with the constant threat of the layers building up putting heavy pressure on you to remove them as quickly as possible. As a result of this, hazard stacking hyper offense was born, with a team consisting of a suicide Spikes lead, a spinblocker (i.e. Gengar), a spinner (usually Starmie) and three other heavily offensive Pokemon. ADV OU is generally considered to be the most balanced metagame, and this is because a lot of the more powerful pokemon were held back by their STAB not matching with their stronger offensive stat, making Normal-type coverage very common in the metagame. However, I'm not here to talk about the common types in ADV, but about the history of entry hazards. Alongside spikes stacking hyper offense, Spikes in conjunction with the new mechanics for Toxic and a substantial reduction in the use of Rest resulted in full stall becoming significantly more effective than in GSC. Stall teams would typically carry either Forretress or Skarmory to lay hazards, a remover such as Forretress or Claydol and a number of pokemon capable of stalling. There's not that much I'm willing to say about ADV, so lets just move into gen 4.
The release of Pokémon Diamond and Pearl brought what were argubly two of the most influential things ever to grace OU without getting banned: Stealth Rock and Heatran. With Heatran being the most common Pokemon in the metagame, it was already obvious that generation four meant business. However, it could also learn Stealth Rock: a move which singlehandedly shaped the viability of a huge number of Pokemon. Stealth Rock is a move which can only be layed down once and deals damage dependent on the type effectiveness of Rock on the Pokemon which has to suffer it - ranging from 3.125% for a 4x resistance such as Lucario to 50% for a pokemon 4x weak to it such as Charizard. With various of the previous Spikes getting the move, it very quickly became overshadowed on the vast majority of teams simply due to how much better Stealth Rock was most of the time, and its influence really showed. With things like Charizard - which had seen use on select teams in previous generations - dropping off of the viability rankings altogether and pokemon which could set, remove and prevent its removal raining supreme. While there were some... debatable Pokemon which were OU by usage due to the move (*cough* Dusknoir *cough*), it brought a new level of strategy that was never seen to the same degree when you could only use Spikes, and it resulted in a significant drop in the viability of Flying-types such as Staraptor (forever BL) due to them no longer being immune to the only entry hazard - instead taking 25% on switch-in (outside of a few exceptions such as Gliscor). However, Stealth Rock wasn't the only new move on the block, with Toxic Spikes also being introduced in the same generation. This move would poison or toxic poison a pokemon on switch in, depending on whether 1 or 2 layers were present - and it, like Spikes, was avoided by Flying-types. In addition, it was absorbed by poison-types and Steel-types were not poisoned due to their immunity to said status. This move never made much of a splash in the metagame due to poor distribution and an effect which was decent at best. However, it wasn't completely unused. With various Pokemon including Forretress - god of all hazards - getting the move, it was used on teams which struggled v.s. stall and balance for its niche of being the only way to reliably toxic poison Celebi and Blissey due to Natural Cure, and it was often a win-con in such matchups as a result. There really isn't much else to say about it really, so on to generation 5!
Not much changed regarding entry hazards in generation 5 aside from it being the first instance of a Pokemon that was both OU by usage that didn't suck ass which was 4x weak to Stealth Rock in Volcarona. There were also a few more Pokemon which could spinblock introduced - most notably Jellicent - and, with the release of BW2, more Stealth Rock users. However, arguably the biggest change regarding hazards was the introduction of Magic Bounce. While it was limited to two less-than adequate users in Xatu and Espeon, the latter managed to carve itself a niche in the metagame. While it was small, it was what ultimately got the ball rolling regarding Baton Pass' viability as a strategy. Espeon was the first Pokemon on Baton Pass teams which could block any of Taunt or Whirlwind. However, the impact which I brought the ability up for was its effect on the way you had to play entry hazards. Magic Bounce was capable of cockblocking the use of any entry hazards when the Magic Bouncer was on the field, and it made it amazing support for Pokemon such as Volcarona, which could take advantage of your side being protected by hazards to, y'know, not take 50% from Stealth Rock. However, it did require prediction, so there isn't much else that I can say regarding it. Its effect wasn't huge, but it saw use nonetheless.
The release of Pokemon X and Y resulted in three things regarding entry hazards. The first was what was simultaneously the most overhyped move in the history of overhyped moves: Sticky Web. In the period which I dub the "oh mah gawd new stuff must hype" period, Sticky Web ran rampant in OU. There was lots of speculation about how it would obliterate the viability of hyper offense and how it was the new best entry hazard. However, neither of these materialised. This is primarily due to Sticky Web's atrocious distribution, with the only viable user being the all-powerful Shuckle
which OHKO's the entire team just by existing, but people realised that you shouldn't fuckle with Shuckle due to Sticky Web not being what it was cracked up to be due to all of its setters being taunt bait, suicide leads or both. This meant it was hard to set repeatedly throughout the match and relied on a team using up two of its teamslots for a spinblocker and Bisharp in order to stand any chance of keeping them on the field. However, the main impact it had was seen in early RU, with Shuckle being banned due to Sticky Web being broken in a metagame with Druddigon (plz ban
Molk) and Shuckle being the only thing that could set it repeatedly due to its bulk. What was by far the biggest news regarding entry hazards was born with the buffing of Defog: a move which, as of generation 6, has the ability to remove entry hazards from both sides of the field which can't be blocked by anything other than Taunt. This was the biggest downfall of Sticky Web, and it is a big contributing factor to the viability of Talonflame and Charizard. It also brought along big changes in the makeup of teams, such as Bisharp becoming one of OU's top dogs due to a large number of favorable changes (Steel-type nerf, Knock Off buff and Defiant acting as a Defog deterrent). Speaking of Bisharp, Defiant and Competitive are now considered to be two of the best abilities in the game due to their utility of deterring Defog. While Competitive never saw any serious use outside of Milotic's short time in RU (please for god sake drop -_-), Defiant is now staple in all of OU, RU, PU, LC and, to a lesser extent, NU due to good users being present in all of said tiers and Defog being commonplace. It also directly affected the viability of what is considered to be one of the most threatening pokemon of BW2: Specs Latios. The change to the move singlehandedly blew Specs Latios' viability away due to it benefitting heavily from having Defog. anyway, I'm bored of talking defog, so I will move on. The final change to hazards of XY occurred in mid XY when Baton Pass got banned. The only viable Magic Bounce user (Espeon) essentially became inviable with the death of Baton Pass, and it resulted in its drop to obscurity. However, just when we thought that Magic Bounce was dead in the water, we were graced with the pleasant surprise that ORAS brought: two brand-spanking new mega evolutions. When they were were introduced into the metagame they revived Magic Bounce - finally giving the ability two much-deserved good users in Mega Sableye and Mega Diancie. These Pokemon have had a profound effect on the way that entry hazards are played. It also gave a new lease of life to something which is currently being talked about in the viability rankings: Shedinja. Mega Sableye was the sole contributing factor to anyone even bothering to put the effort into trying out Shedinja, and I personally can't wait for the main ladder to return so that I can try out Shedinja stall. Aside from this, Magic Bounce functions the same as before, except now in the hands of two capable users.
That was a brief history of entry hazards by me. I have probably missed a lot and messed a little info up with generation 3, but all in all I enjoyed writing that and hope that someone can be bothered to read this wall of text :)