Hey there! Cool team so far! Mega Medicham is a huge threat in the metagame right now and you've picked a lot of good partners for it. There are a good number of threats, however, to what you have so far that I think I can patch up.
I've noticed that the team so far is completely walled by Mega Sableye, which isn't good for a team with Mega Medicham since it can't touch Sableye at all. Mega Charizard X is another big problem because it outspeeds everything even without a boost. If it comes in on Amoonguss after something's been put to sleep or a Volt Switch from Rotom-Wash, it can get a free Dragon Dance. The only thing that can live a hit from Mega Charizard X is Rotom-Wash, which is likely to get worn down over the course of the match. Swords Dance Garchomp can also be pretty devastating if it gets the chance to set up. Rotom-Wash can't reliably burn it if its Lum Berry--a common item on Swords Dance Garchomp--is still intact because it gets 2HKOed by +2 Dragon Claw. Other minor threats would be Mega Gardevoir and Mega Heracross since there aren't any safe switch-ins for them so far, although they can be revenge killed which is why they're not huge threats.
I've actually thought of two possible variations for this team. There are some pros and cons to each variation that I'll list at the end of this answer, so you can pick the one you like the most or the one you think is best for you to use. The first version of the team is pretty standard, but the second version is a little more unique.
Version 1
For this version, I suggest replacing Garchomp with Choice Scarf Landorus-Therian. I thought that this would be a more reliable answer to SD Chomp and Mega Charizard X as well as a switch-in for Mega Heracross. This also gives some speed to this team and the Choice user that you were thinking of using. Additionally, this adds a second pivot alongside Rotom-Wash to form a Volt-Turn core which is great for not only bringing in Mega Medicham safely, but for wearing down teams a bit with repeated Volt Switches and U-Turns to ease the late-game clean with Mega Medicham.
Landorus-Therian @ Choice Scarf
Ability: Intimidate
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
- Earthquake
- Stone Edge
- Superpower
- U-turn
The team still doesn't have an answer to Mega Sableye or a safe switch-in to Mega Gardevoir. Because of this, I suggest using specially defensive Heatran as your 6th pokemon for this version. Heatran is a great counter to Mega Sableye and can switch into Mega Gardevoir's Hyper Voice and Psyshock as well as Will-O-Wisp if it carries it, but has to be wary of Focus Blast. Since the removal of Garchomp took out your hazard setter, specially defensive Heatran works over other sets since it runs Stealth Rock.
Heatran @ Leftovers
Ability: Flash Fire
EVs: 252 HP / 188 SpD / 68 Spe
Calm Nature
- Lava Plume
- Toxic
- Taunt
- Stealth Rock
Version 2
For this version, I tried to think of how to make Garchomp work in case you didn't want to change anything. I felt like the best way of doing that was using offensive Stealth Rock Garchomp over defensive Garchomp. Offensive Garchomp can be a great early-game wallbreaker that can help weaken bulky ground types and fairy types with the help of Swords Dance. These pokemon would normally be good switch-ins to defensive Garchomp, and weakening them helps Mega Medicham out a lot with cleaning up teams late-game since they can be used when they're at full health to switch into Medicham.
Garchomp @ Lum Berry
Ability: Rough Skin
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
- Stealth Rock
- Earthquake
- Dragon Claw
- Swords Dance
After this change, there's still the same problems as the first version as well as a reliable answer to opposing Swords Dance Garchomp and Mega Charizard X. I still wanted to have Heatran as the final pokemon, but I decided on using a pretty interesting Heatran set that not many people expect. For this version, I suggest using Choice Scarf Heatran as your 6th pokemon. Scarf Heatran's a pretty uncommon set, so in my experience, whenever people see Heatran on the opponent's team, they don't often check for a Scarf set. This can lead to some surprise KO's if the opponent chooses to leave their pokemon in. This set can revenge kill many of the offensive threats that I mentioned and gives you the extra speed that the team needs.
Heatran @ Choice Scarf
Ability: Flash Fire
EVs: 28 HP / 252 SpA / 228 Spe
Timid Nature
- Fire Blast
- Flash Cannon
- Hidden Power Ice
- Stone Edge
Finally, a minor change, but I think it's better for both versions of the team to be running Thunder Punch over Bullet Punch on Mega Medicham. Slowbro could be a problem to this team if they run Psyshock for Amoonguss, although Bisharp can check it. Adamant Thunder Punch 2HKOs Slowbro from full health. This also makes Mega Medicham extremely scary for teams to face since Electric and Ice coverage on it along with its STAB High Jump Kick hits so much in the metagame for huge damage.
Version 1
Pros
- More reliable switch-ins to offensive threats
- More momentum to bring Mega Medicham in
- Can play more safely
Cons
- More changes to the team
- Less offensive pressure
Importable
Amoonguss (M) @ Black Sludge
Ability: Regenerator
EVs: 248 HP / 168 Def / 92 SpD
Bold Nature
IVs: 0 Atk / 30 SpA / 30 Spe
- Spore
- Giga Drain
- Clear Smog
- Hidden Power [Fire]
Medicham (F) @ Medichamite
Ability: Pure Power
EVs: 252 Atk / 4 Def / 252 Spe
Adamant Nature
- High Jump Kick
- Ice Punch
- Fake Out
- Thunder Punch
Bisharp (M) @ Black Glasses
Ability: Defiant
Shiny: Yes
EVs: 252 Atk / 52 SpD / 204 Spe
Adamant Nature
- Knock Off
- Iron Head
- Sucker Punch
- Pursuit
Landorus-Therian @ Choice Scarf
Ability: Intimidate
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
- Earthquake
- Stone Edge
- Superpower
- U-turn
Heatran @ Leftovers
Ability: Flash Fire
EVs: 252 HP / 188 SpD / 68 Spe
Calm Nature
IVs: 0 Atk
- Lava Plume
- Toxic
- Taunt
- Stealth Rock
Rotom-Wash @ Leftovers
Ability: Levitate
Shiny: Yes
EVs: 248 HP / 252 Def / 8 Spe
Bold Nature
IVs: 0 Atk
- Volt Switch
- Hydro Pump
- Will-O-Wisp
- Pain Split
Version 2
Pros
- Less predictable with the uncommon Scarf Heatran
- More innovative
- Less changes to the team
- More offensive pressure to support Mega Medicham
Cons
- Less reliable switch-ins to offensive threats
- Requires a more aggressive playstyle (i.e. more prediction-heavy, more risky plays)
Importable
Amoonguss (M) @ Black Sludge
Ability: Regenerator
EVs: 248 HP / 168 Def / 92 SpD
Bold Nature
IVs: 0 Atk / 30 SpA / 30 Spe
- Spore
- Giga Drain
- Clear Smog
- Hidden Power [Fire]
Medicham (F) @ Medichamite
Ability: Pure Power
EVs: 252 Atk / 4 Def / 252 Spe
Adamant Nature
- High Jump Kick
- Ice Punch
- Fake Out
- Thunder Punch
Bisharp (M) @ Black Glasses
Ability: Defiant
Shiny: Yes
EVs: 252 Atk / 52 SpD / 204 Spe
Adamant Nature
- Knock Off
- Iron Head
- Sucker Punch
- Pursuit
Garchomp @ Lum Berry
Ability: Rough Skin
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
- Stealth Rock
- Earthquake
- Dragon Claw
- Swords Dance
Heatran @ Choice Scarf
Ability: Flash Fire
EVs: 28 HP / 252 SpA / 228 Spe
Timid Nature
IVs: 30 HP / 30 Def
- Fire Blast
- Flash Cannon
- Hidden Power [Ice]
- Stone Edge
Rotom-Wash @ Leftovers
Ability: Levitate
Shiny: Yes
EVs: 248 HP / 252 Def / 8 Spe
Bold Nature
IVs: 0 Atk
- Volt Switch
- Hydro Pump
- Will-O-Wisp
- Pain Split
Hopefully either of these teams work out well for you. Good luck with your future battles!
