Hey there! The team looks really solid. The biggest problem I can see is a lack of a win condition. Gardevoir is great at wearing down teams, particularly against stall and balance, but there's nothing on your team that's taking advantage of that to finish the game after everything's been weakened.
I don't think Mamoswine is doing too much for this team. It's good for being able to revenge kill things with Ice Shard, but I prefer having something else become a revenge killer and adding a win condition instead. I feel like SubCM Keldeo is an interesting win condition that fits well on this team because Mega Gardevoir can hit a lot of Keldeo's defensive checks hard, and it lures in steel types that Keldeo can switch into and set up a substitute on after its checks have been weakened enough. Having Keldeo on this team also takes some pressure off of Rotom-Wash since it's currently the only check to Weavile, which with Rotom-Wash gone can be very problematic to the current team. Because of all this, I suggest replacing Mamoswine with SubCM Keldeo.
Keldeo @ Leftovers
Ability: Justified
EVs: 4 Def / 252 SpA / 252 Spe
Timid Nature
IVs: 0 Atk
- Substitute
- Calm Mind
- Scald
- Secret Sword
Unfortunately, with Mamoswine gone, the team loses its main revenge killer and thus, the team loses any form of speed control. To remedy this, I suggest changing Landorus-Therian's set from defensive to scarf.
Landorus-Therian @ Choice Scarf
Ability: Intimidate
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
- Earthquake
- Stone Edge
- Knock Off
- U-turn
Now that the team has lost its rocker, Heatran should be changed to the specially defensive set. I think this Heatran set is better for the team, anyway, because you don't really need Heatran to provide offensive pressure since the team has enough of it with Gardevoir, Latios, and now Keldeo (Mamoswine also provided some offensive pressure for the team). Also, I don't think the stallbreaker set fits on this team either because Mega Gardevoir already breaks through stall pretty well. As a final note, Air Balloon isn't necessary on this team since you have Rotom-Wash and Landorus-Therian to check ground types.
Heatran @ Leftovers
Ability: Flash Fire
EVs: 252 HP / 188 SpD / 68 Spe
Calm Nature
IVs: 0 Atk
- Lava Plume
- Toxic
- Protect
- Stealth Rock
Finally, for some minor changes, replace Will-O-Wisp with Taunt on Mega Gardevoir since you already have Rotom-Wash for burning things on the switch, and change Latios' EVs to 252 SpA / 252 Spe / 4 Def. As far as I'm aware of, the extra defensive EVs aren't doing anything important, but correct me if I'm wrong.
HP Ground Serperior could cause the team trouble after these changes, but I think HP Fire variants are more common and you can still play around it as long as you don't give it a chance to safely fire off a Leaf Storm. Hopefully these changes helped the team out and good luck with it in battles!
Summary of Changes:
>
Scarf>Defensive
Defensive Tran > Offensive Tran
Taunt > Will-O-Wisp
change EVs
