Okay sorry this took me a little while, but I really like your team. Just Mega-Medicham seems a little out of place look at your team on team Magma builder you have a rock and a electric weakness. So I kept that in mind when I did this RMT. Changes will be in Bold.
Ludicolo (M) @ Assault Vest
Ability: Swift Swim
Level: 50
EVs: 252 HP / 188 Def / 68 SpA
Modest Nature
- Scald
- Ice Beam
- Fake Out
- Giga Drain
He is perfect. Nothing to change, it is a very standard set.
Politoed @ Sitrus Berry/ Eject Button
Ability: Drizzle
Level: 50
EVs: 252 HP / 76 Def / 76 SpA / 100 SpD / 4 Spe
Calm Nature
- Scald
- Icy Wind
- Helping Hand
- Protect
Yes there is a surprise factor with rain dance, but truly it is wasted slot. You can switch or possibly give Politoed the Eject Button item so he can spread drizzle more. Helping Hand is to boost those Pokemon on your Team that will be picking up the KOs.
Aegislash @ Leftovers
Ability: Stance Change
Level: 50
EVs: 236 HP / 252 SpA / 20 Spe
Modest Nature
- Wide Guard
- King's Shield
- Flash Cannon
- Shadow Ball
Wide Guard is a great move, preventing Rock Slides for Talonflame, and Hyper Voices (fairy) for Hydreigon. It also blocks Heat Waves and Earthquakes for itself.
Hydreigon @ Choice Specs
Ability: Levitate
Level: 50
EVs: 84 HP / 12 Def / 236 SpA / 4 SpD / 172 Spe
Modest Nature
- Draco Meteor
- Heat Wave
- Dark Pulse
- Earth Power
Really this is more of an opinion but spread damage is crucial is VGC. Heat Wave is slighty better I think, but Flamethower is of course a very good substitue.
Talonflame @ Life Orb
Ability: Gale Wings
Level: 50
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Brave Bird
- Flare Blitz
- Overheat/U-turn/Tailwind
- Will-O-Wisp
I swapped the Band for Life Orb as it allows some variables in your sets. Will-O-Wisp to cripple those Physical attackers. Your choice of Overheat, U-Turn, or Tailwind. I think Overheat has the most Potential, as it is his only special move, so that stat drop will not weaken you.
Yes Medicham is an underrated Mega, but there are better options, even more so on a rain team. Medicham compounded several weaknesses, I took these into account and I think I found the perfect Mega.
Swampert @ Swampertite
Ability: Damp --> Swift Swim
Level: 50
EVs: 104 HP / 252 Atk / 152 Spe
Adamant Nature
- Waterfall
- Earthquake
- Superpower/ Brick Break/ Ice Punch / Rock Slide
- Protect
A very good Mega for in the rain, has loads of offensive power. The EVs are utilized to give Swampy his maximum damage output and bulk. Giving Mega Swampert 152 Speed EVs is for out speeding Pokemon in rain not faster than Mega Sceptile, his arch enemy. Waterfall is mandatory. Earthquake is great, and you have a flying type, and a levitate user on the team so that could always be useful. You could also just protect with your ally Pokemon. The last move is your choice. I would recommend Superpower or Rock Slide for power/utility. Brick Break if you don't like the stat drop of Superpower. Ice Punch wouldn't be great because you have 2 other Pokemon with Ice moves. Protect because this is doubles and you want your Mega to last.
If you want to keep Medicham use this set instead.
Medicham @ Medichamite
Ability: Pure Power
Level: 50
EVs: 192 HP / 252 Atk / 64 Spe
Adamant Nature
- Bullet Punch -Can be used more than once and gives him priority throughout the battle.
- Drain Punch/Force Palm -Lots of Pokemon use Protect in double battles and if you hit a Pokemon using Protect with High Jump Kick you will lose half your HP. The HP gained from Drain Punch is nice although Force Palm can cripple fast Pokemon with Paralysis.
- Zen Headbutt -The flinch chance is better than the higher accuarcy.
- Detect -Same as protect, just a little rarer.
I hope you liked the changes, and truly you did build a very good team to start with. Only 1 Pokemon change and other very minor tweaks were needed. I hope you do much better, with your new team. Have a great Summer!
-Unstoppable