Gardevoir

Synchronize
When statused, the enemy is also statused. Can pass nature to wild Pokémon.
Trace
Copies foe's Ability.
Type Tier
Psychic BL
Statistics
Min- Min Max Max+
HP
68
- 277 340 -
Atk
65
149 166 229 251
Def
65
149 166 229 251
SpA
125
257 286 349 383
SpD
115
239 266 329 361
Spe
80
176 196 259 284
Name Item Ability Nature

Support

Leftovers Trace Modest
Moveset EVs
~ Will-O-Wisp
~ Wish
~ Psychic
~ Thunderbolt / Focus Blast / Shadow Ball
252 HP / 48 SpA / 176 SpD / 32 Spe

Gardevoir stands out as a support Pokémon, with a large movepool and the ability to attack if the need arises. You mainly want to switch this in to a relatively passive Pokémon, or unSTABed special attacks, as even though it has 115 base Special Defense, its 68 base HP means it can't take very many powerful hits. Support the team with Will-O-Wisp, burning any Physical attackers that attempt to switch in (such as Snorlax, Metagross and Tyranitar, who are all common switches to Gardevoir). Thunderbolt covers Gyarados and Skarmory; Focus Blast is a more proactive solution for taking care of Weavile and Tyranitar, and it dents Heatran pretty badly; Shadow Ball helps against Azelf and other Psychics.

Trace gives Gardevoir much more of a chance to switch in or to help the team than Synchronize does. Electivire is an excellent Pokémon to switch Gardevoir into, as it can't 2HKO you, and you can burn it to stop a sweep. Volt Absorb/Water Absorb Pokémon are your friends, you can "wall" Flash Fire Pokémon such as Heatran, and if you really want to take a risk, you can auto-Intimidate things like Salamence and Gyarados; just be careful to not switch into Choice Banded attacks.

Name Item Ability Nature

Double Status

Leftovers Trace Modest
Moveset EVs
~ Hypnosis
~ Will-O-Wisp / Thunder Wave
~ Psychic
~ Thunderbolt / Focus Blast / Shadow Ball
252 HP / 48 SpA / 176 SpD / 32 Spe

The idea's been around since Red/Blue/Yellow, but it still works in Diamond/Pearl! Sleep something, then immediately use Will-O-Wisp or Thunder Wave as they (hopefully) switch to something else. It's very basic prediction, but you can cripple a third of the opponent's team immediately if you can pull it off. Always helpful.

You can use Wide Lens or Zoom Lens to boost the accuracy of Hypnosis, Will-O-Wisp and Focus Blast, although Leftovers is usually a better choice.

Name Item Ability Nature

Calm Mind

Leftovers Trace Timid
Moveset EVs
~ Calm Mind
~ Psychic
~ Thunderbolt / Focus Blast / Shadow Ball
~ Will-O-Wisp / Wish
56 HP / 252 SpA / 200 Spe

Gardevoir makes a nice Calm Minder, as it can take a few hits while it sets up. Raising Special Defense and burning physical attackers can put your opponent in a very bad spot. Wish helps to heal while setting up.

Other Options

Destiny Bond works well on Gardevoir, since you can trick Blissey into trying to kill you with Seismic Toss. Taunt allows Gardevoir to do some damage to stall based teams and combos well with Destiny Bond. Trick Room is another way to play with Speed, and it helps with Gardevoir's general theme of team support. Just give it Quiet instead of Modest, and set its Speed IV to 0. Gardevoir certainly has a big enough movepool to use Choice Specs, but you'd be ignoring the great support movepool, and something like Alakazam is better suited for that anyway. If you find that you're able to get Gardevoir into many passive Pokémon who are using support moves, consider Snatch to take them for yourself. There's even Healing Wish if you want to "revive" a nearly fainted Pokémon. Mean Look can trap unsuspecting Pokémon, netting you an easy switch. Really, Gardevoir has a ton of options, and that's what makes it a decent Pokémon.

EVs

Max HP and give it a good serving of Defense and Special Defense, using a Modest nature for Special Attack. Outspeeding Tyranitar means you won't instantly lose a Pokémon if it manages to switch in to a Psychic or Wish. You can give Gardevoir 104 Speed EVs to get 222, outspeeding a max Speed Adamant Tyranitar by 1 point, or 192 EVs to outspeed Jolly Tyranitar by 1 point. Unless you're running Salac Berry or Choice Scarf, more Speed isn't really going to help much, as all the things Gardevoir would like to outspeed are much too fast for it to catch anyway. You may want to skimp on the Defense and rely on Will-O-Wisp to protect you, but being able to pull off a few tricks like stopping Electivire or Intimidating Gyarados is always nice, and because it has low Defense, EVs there reduce damage by more than they would in Special Defense.

Opinion

Don't make the mistake of trying to play Gardevoir like you would Alakazam or Azelf. Gardevoir's allure is its ability to take a few hits and support the team with status and healing moves. Of all of the pure Psychic-types, Gardevoir has the least to fear from Pursuit thanks to her ability to fire off Will-O-Wisp to cripple most physical attackers and batter Heracross with a powerful STAB Psychic. Although it is often overlooked in favor of Cresselia for a defensive/supporting role, or Azelf and Alakazam in the offensive department, Gardevoir is a fine Pokémon with many useful move options. Having the rare and incredibly useful Trace ability is also a great advantage.

Counters

Weavile and Tyranitar are the two biggest counters, but neither can switch into a Will-O-Wisp, which Gardevoir will almost always have. Still, if Gardevoir kills something, you can revenge kill it. Houndoom is boosted by Will-O-Wisp and can Pursuit Gardevoir as well, but Thunderbolt will do a lot of damage if you mispredict. Heatran is a great offensive threat to bring in on Gardevoir, as it, too, absorbs Will-O-Wisp with Flash Fire, resists Psychic and Grass Knot, and has the Special Defense to shrug off Thunderbolt. If you don't want to take damage from it, special walls such as Blissey and Cresselia work, but Gardevoir will just Wish and switch out anyway. Your best bet isn't to bother switching to a "counter", since it's just going to use a support move. Instead, take advantage of its low Speed and HP.