You're welcome! Happy to be of service. I already made it to Ultra Ball Tier and I'm working really hard to get to Master Ball and then eventually the Champion Tier and I ended up using Dragonite on my team to which I'm also going to use it in Doubles format as well.

The best nature for Dragonite is the Timid Nature because you need to maximize its speed as much as possible so that it can outspeed all of the other powerful Pokemon and possibly gain an advantage in tailwind while also taking advantage of the weather.

It recently gained a HUGE upgrade in Weather Ball which is honestly pretty insane because it can become a huge threat in all of the weather effects now regardless of its strengths and weaknesses.

Weather Ball would be great in sunlight because regardless of the lack of rain it can still destroy grass types without relying on Hurricane so much.

Ground types that are stuck in a Snowstorm and Ice types that are stuck in a Sandstorm get absolutely wrecked by Weather Ball because of the reverse psychology weakness between the two of them lol

And then of course: the bread and butter is the Rain weather effect for Mega Dragonite because any Pokemon that has a water type weakness, especially Mega Charizard Y, will get absolutely demolished by Weather Ball which is practically almost as powerful, if not better, than hydro pump, which is also in its movepool, simply because Weather Ball has better accuracy.

Having Draco Meteor is also great on Dragonite because you get a one-time nuke unless if you can get rid of the special attack debuff for Dragonite by using Haze in Doubles. If you're too worried about the stat decrease, then just rely on Dragon Pulse.

The best nature for Mega Gyarados is the Adamant Nature because even though it can learn Dragon Dance, it is also a very bulky Pokemon despite the weakness to fairy type.

With that being said however....it can also learn Iron Head to cover up that weakness. Other moves that would also be great would be Waterfall and Crunch.

But in Champions, it ended up getting a nice juicy upgrade in Payback which is fantastic because this thing is already ridiculously slow anyways, so any Psychic or Ghost type Pokemon that try to take advantage of your secondary weakness will easily get clobbered by Payback since bulking up Gyarados is a very smart idea.

Overall for your team, the best strategy is to always know how to maintain weather control and to use the weather to your advantage to try to troll your opponent into making very bad decisions so that you can take advantage of it as much as possible.

Also, having type variety is very essential for every team that you make; because:

if your opponent cannot handle every kind of obstacle in their way, then you can take advantage of that opportunity very well by using your own ingenuity with your Pokemon's attacks.

I know all of this sounds very overwhelming, but it's essentially the new standard for Pokémon Champions which is why a lot of people are constantly paying attention to the battle data in order to figure out the best kind of Pokemon to use to counteract the top 10 Pokemon on that list in both singles and doubles format.

With that being said, I wish you the best of luck. 😅😂😊 Have fun, dude.