Mega rayquaza is a BEAST with weakness policy!
Rayquaza @ Weakness Policy
Ability: Air Lock
Shiny: Yes
EVs: 4 Atk / 252 SpA / 252 Spe
Hasty Nature
- Thunderbolt
- Meteor Beam/Earth Power
- Dragon Pulse/Iron Head/Outrage
- Dragon Ascent
Now you were probably expecting a physical rayquaza? Right? Sorry to disappoint you, but hey, a weakness policy special attacker isn’t so bad. This set utilises Rayquaza speed when using meteor beam. Meteor beam can take down Ice types in a flash; boosting its Special Attack with an additional weakness policy will make your Rayquaza unstoppable. Meteor Beam has a base power of 120 and a reasonable accuracy of 90.
The only downside is that Rayquaza’s defence is not so good against Dragon types or Electric types that might sweep your team during the next turn. So an alternative to this is:
Earth Power has a 10% to lower the target's Defense by 1 stage, it can also take out Rock, Steel, Fire, and Electric types that might KO you.
Thunderbolt for coverage, preferred Over thunder due to better accuracy and it still has a 10% chance of paralysis, so better than nothing, am I right?
Dragon pulse… yeah, no Draco Meteor (as it would defeat the purpose of weakness policy). Dragon pulse is more of a replacement for outrage with a decent accuracy of 100; it’s the shadow ball of dragon types. However, most do not consider Dragon Pulse worthwhile as it has no additional effects and a low base power compared to other options for Rayquaza, although running in a weakness policy set with a SpAtk EV build isn’t a cause for too much to complain; outrage is an excellent physical stab for Rayquaza, given its 100 accuracy and base power of 120, it does get confused afterwards, but it’s pretty much worth it if you want to get rid of Dragon types.
Iron head is also another option because it gets rid of most of the weaknesses Dragon has, such as Fairy, Rock, and Ice; I would use it over Iron tail due to the much better accuracy, despite the reduced power. However, because it isn’t that good in power, in my opinion, I would keep the other options. But it is a good coverage move.
Dragon Ascent is Rayquaza’s main stab move and gives Rayquaza the ability to Mega Evolve, mega Rayquaza's weakness policy is a beast, and with it’s high speed, Meteor Beam or Other moves such as dragon ascent wouldn’t be a problem, just Mega Evolve, use dragon ascent, and boom, swept your entire enemy team.
My first time answering on PokeBase, I might do more answering moveset builds.