Dragonite
@ weakness policy
Ability: Multiscale
252 HP / 4 Atk / 252 Spe
Nature: Hasty / Naive
Agility
Fire Blast / Fire Punch
Earthquake
Dragon Claw
Once this badboy, gets set up, very few things are taking any hits from it. The idea is to agility with multiscale intact, because this dragonite needs the speed boost to be effective. Thanks to multiscale and full HP investment, dragonite can tank even most ice attacks, allowing weakness policy to activate. Even with zero investement, dragonite's attack stats reach 608 Atk and 474 SpAtk after activation. Agility gets your speed around 580, so nothing practical is outspeeding you.
The attacks are straight forward, giving dragonite nearly perfect neutral coverage. Dragons simply can't afford to be locked into outrage this gen, so dragon claw is chosen instead. Earthquake gives the standard great coverage next to dragon, and hits plenty of things super effectively itself. The choice between Fire Punch or Fire Blast is really up to you, Blast is listed first because it allows dragonite to avoid things like iron barbs and king's shield. It also gives you the 2HKO on mega aggron, which could tank EQ with it's titanic defense stat. Once extremespeed is released, this set would really appreciate its priority and it could be considered over earthquake.
This dragonite functions much better in the early game, smashing holes in unprepared teams, with dragonite essentially have a shell smash boost within the first couple of turns if played correctly. Remember that you have no form of recovery, so if you want to save it for later in the match, you need a way to remove SR. Weakness policy in general is a one shot per match thing; so once you go for it, there is no point to switch out as the boosts disappear and you're left with no item.
Partners: Like any sweeper, this dragonite loves screens to help it out, and light clay klefki is a great partner. It resists all of dragonite's weaknesses, taking rock / ice / dragon / fairy attacks with ease, and setting up priority screens that can essentially function as a second shot at multiscale. If something happens and dragonite needs to be saved for later, Forretress is a good spinner that pairs well with dragonite, and can even throw down hazards to break those sashes this set hates. Defoggers such as empoleon can be used in a pinch, but dragonite appreciates hazards on the other side of the field.
Checks and counters: Once this dragonite is set up, basically nothing is switching into this without taking massive damage. Bronzong can force dragonite to guess which move to use and hurt it badly with gyro ball, but a good (or lucky) choice by your opponent is still a OHKO. There are three main ways to deal with this dragon: status, speed and priority. Once you realize that this set isn't sub or lum berry, paralyzing it should be a top priority. This dragon has no priority itself, so once it's para'd it goes down quickly, although whatever paralyzes it will probably sacrifice itself in the process. Burn can be used in a pinch, as a burn at +2 returns dragonite to normal attack levels. Similarly, priority can be used, but be aware that dragonite resists fighting and water, limiting your options. Like many boosting sweepers, unaware quagsire stops it dead in its tracks and ice beams for the OHKO. In a bit of a final uncommon counter, Porygon2 can come in and trace multiscale, survive a hit and OHKO with ice beam.