What effect did this Pokemon have on the metagame?
In every generation of 1v1, Snorlax is a menace. In fact, it is banned in all gens but BW and RBY. In SS, as in every other gen, Snorlax’s insane bulk, good attack, and great movepool served it extremely well. At the same time, the power level in SS is generally lower than that of the past two generations, making Snorlax unmanageable. Almost no 100% counters existed, with many matchups coming down to a setguess or a 50/50. Strong, physical Fighting types, such as Urshifu and Sawk, could beat it reliably enough, but little else could handle it, meaning Snorlax’s presence greatly restricted teambuilding and stifled creativity.
How was this Pokemon used?
Snorlax had 3 primary sets - Custap, Choice Band, and Stall/Chople. With its new tool in Encore, Snorlax's Custap set became particularly powerful this generation. After using Belly Drum to bring itself into Gluttony Custap range, Snorlax could either attack or use Encore on the next turn. Choice Band Snorlax had insane coverage, including Heat Crash for Genesect and other Steels, Gunk Shot for Fairies, and numerous niche options for whatever matchups it needed to cover. All of these coverage options were placed alongside its devastating STAB Giga Impact. Finally, Stall Snorlax, equipped with a Chople Berry, was able to defeat many Choiced physical attacker by simply clicking Counter while also acting as a blanket special wall with Amnesia.
Sets:
https://pokepast.es/ec67dd64e521c289
What caused it to have a significant impact?
Snorlax's tremendous bulk, high attack, insane coverage, and access to Encore proved too much for the SS metagame to handle. It had very few reliable counters, so its presence restricted teambuilding greatly. It forced setguessing in almost every preview where it appeared, leading to outcomes where Snorlax wins even though the opponent correctly predicts it to come out. Snorlax had an extreme centralizing effect on the metagame, with every team being made to run one of its few hard counters or else deal with an absolute headache in team preview.
How do/did you deal with this Pokemon in 1v1?
Urshifu, Sawk, and other Fightings were pretty much the only reliable counters to Snorlax. Even then, if using any Fighting other than Sawk, one had to take care not to get Countered by Chople Snorlax. Otherwise, counters were generally set-specific and had to guess which set an opposing Snorlax was running. For example, Pluck Braviary was occasionally used as an option to defeat Custap Snorlax, but it was unable to handle Choice Band. Taunt users could handle Stall and sometimes Custap, but often lost to Choice Band. Pokemon with sufficient physical bulk and appropriate typing to handle Choice Band, meanwhile, would often find themselves losing to one or both of the other sets.