Ahh, it feels good to be back.
Anyways, your team is pretty solid. Trick Room is fun, too. :3
Miltank (F) @ Leftovers
Ability: Scrappy
EVs: 252 HP / 252 Def / 4 Spe
Impish Nature
- Milk Drink
- Heal Bell
- Curse
- Body Slam
This, I see no problem with. Though, are you sure you want to use a Pokemon with base 100 Speed on a Trick Room team? I see the strategy with Curse, but you're gonna be pretty fast for the first two turns, so a slow Pokemon can easily come in and destroy your poor Miltank.
Ninetales @ Air Balloon
Ability: Drought
EVs: 4 HP / 252 SpA / 252 SpD
Calm Nature
- Solar Beam
- Nasty Plot
- Will-O-Wisp
- Heat Wave
Again, a Pokemon with 100 base Speed does not belong on a Trick Room team. This one doesn't even have anything going for a low speed stat. Though I can see this working as a backup sweeper if TR ever expires and you don't have something to set it up.
Ampharos (M) @ Ampharosite
Ability: Static
EVs: 252 HP / 4 Def / 252 SpA
Quiet Nature
- Cotton Guard
- Thunderbolt
- Dragon Pulse
- Hidden Power [Ice]
Quiet Nature slows Ampharos down even more, which is very useful when using Trick Room. I changed Discharge to Thunderbolt, as Paralyzed Pokemon have their Speed decreased by 75%. You sure you want that when you need to be the slowest? I also changed Heal Bell to Dragon Pulse because Ampharos needs that extra STAB to take care of Pokemon like Goodra, who eat up HP Ice.
As for the other Pokemon, I see no problem with them. Though, is there a reason your Gardevoir only has EVs in Special Defense?
P.S. Sorry if this isn't super helpful. I haven't been on here in a while, I haven't seen this in action, and it's easier for me to rate it while it's in a battle rather than guessing.