If you're playstyle is just to go kill, that playstyle fits the description of a hyper offense team. HO teams operate by setting up hazards, having at least two wall breakers, and having at least two endgame sweepers. These teams do not waste time with using toxic or thunder wave or anything really. The put in hazard, they boost, they kill
Just like with any other team, ho teams also need some type of synergy and typically, that takes the form of offensive synergy where the team members overwhelm their shared checks or with one team member being able to deal with a teammate's check and vice versa, sometimes even both
For starters, the best way to gain an idea is to look at a tier's viability rankings. That will give you a rough idea of how each Pokemon fares in the tier. The keyword is "rough idea" because you'll still need to test it out for yourself. For reference, here is the viability rankings for national dex. Often times, before starting to build a team and once you find out what playstyle you're comfortable with, checking the sample teams is always a good idea. The sample teams are made by high level players of the tier to give newer players an easier time learning the tier
I'll try to analyze this sample team for national dex. As you can see, this is a hyper offense team for it have no defensive Pokemon but it has offensive synergy. Koko serves as a support Pokemon to enable Valiant, Moth, and Hawlucha, all of which can overwhelm a common check Toxapex or Gliscor. Due to the nature of the mons on the team, aside from the two support Pokemon, all four can serve as both a wallbreaker and sweeper even though that's not their main role. Making this type of synergy for a hyper offense team is crucial or you're just gonna thud to other teamstyles
to build a hyper offense team, you first need a hazard setter. You need this because the lower the enemy's hp is the easier it is to kill, well duh that's obvious. After that, you need to think of a Pokemon, either a wallbreaker or endgame sweeper, and build your team around that. Building your team around a Pokemon refers to putting in teammates that can support that mon thus creating the synergy I spoke of. Going back to that sample team I put in, the general idea of that team is to use the robot Pokemon. Tapu Koko supports the robots so its role is dedicated to supporting them. Hawlucha has been a natural partner for terrain teams since it can use a seed to immediately trigger unburden and because it gets taunt, it can shut down walls and boost to its little heart's content
Of course, it doesn't have to be built strictly around one Pokemon, a team can be and often is built around a core of Pokemon, which is two or three mons that naturally synergize with each other whether offensively or defensively. A good example is the SkarmBliss combo. This core is sht these days but several generations ago, this was a solid defensive core because Skarmory is often the bane of physical attackers while Blissey is the bane of special attackers, thus the two synergize quite well
Perhaps most important of all, if you're one of those players who just wants to use their favorites in the tier, you're not gonna find much success with any team unless said favorites are those who are viable at all. Basically, those who go "oh I wanna use Morpeko because it's cute I don't care about winning" or some nonsense like that. The thing people need to understand is when your elo is >1400, anything can work. It's a free for all down there where people use stupid sht and can get away with winning because nobody uses those trash mons and can catch people off guard. When playing against an average player at >=1500 elo, that's where players have a good idea of the tier, knows how it works, and can play around those stupid sht mons. In simple terms, what I'm saying is you shouldn't use Pokemon solely because they're your favorites
Now, I am not saying it is impossible to find a niche for some lower tier or even just downright trash Pokemon. There is even a dedicated thread to this very topic in the gen 9 ou forums. However, to find a genuine niche like this needs a lot of metagame knowledge and more importantly, having been built several teams. Once you have built several teams, you will often find a hole in it that can't easily be patched by a Pokemon that's good in the tier so you have to dip to the depths of the lower tier to find something that can patch it. For newer players, the odds of successfully pulling this off is next to zero so, just focus on learning the tier, make trial and errors, test the team, and do adjustments
