Even before the existence of Eviolite people were starting to pass up Porygon-Z for its pre-evolution. Porygon 2 is one of the most well-boosted Eviolite users, like other Pokemon that were originally final stages. Access to Electric- and Ice-type moves gives it well-rounded coverage, and a couple good abilities mean it has the ability to turn things around.
Porygon 2 #233HP: 85
Atk: 80
Def: 90
SpA: 105
SpD: 95
Spe: 60
Level-Up moves
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[LEFT]--Conversion 2
--Tackle
--Conversion
--Defense Curl
Lv7 Psybeam
Lv12 Agility
Lv18 Recover
Lv23 Magnet Rise
Lv29 Signal Beam
Lv34 Recycle
Lv40 Discharge
Lv45 Lock-On
Lv51 Tri Attack
Lv56 Magic Coat
Lv62 Zap Cannon
Lv67 Hyper Beam
[/LEFT]
Machine moves
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[LEFT]TM03 PsyShock
TM06 Toxic
TM10 Hidden Power
TM11 Sunny Day
TM13 Ice Beam
TM14 Blizzard
TM15 Hyper Beam
TM17 Protect
TM18 Rain Dance
TM21 Frustration
TM22 SolarBeam
TM24 Thunderbolt
TM25 Thunder
TM27 Return
TM29 Psychic
TM30 Shadow Ball
TM32 Double Team
TM40 Aerial Ace
TM42 Facade
TM44 Rest
TM46 Thief
TM48 Round
TM57 Charge Beam
TM68 Giga Impact
TM70 Flash
TM73 Thunder Wave
TM77 Psych Up
TM85 Dream Eater
TM87 Swagger
TM90 Substitute
TM92 Trick Room[/LEFT]
Gen IV Tutor Moves
(Pt/HG/SS) Icy Wind
(Pt/HG/SS) Last Resort
(Pt/HG/SS) Signal Beam
(Pt/HG/SS) Snore
(Pt/HG/SS) Swift
(Pt/HG/SS) Trick
(Pt/HG/SS) Zen Headbutt
(HG/SS) Gravity
(HG/SS) Pain Split
(HG/SS) Role Play
Porygon 2 -> Double Battles
->Red Mage<-
Porygon 2 @ Eviolite
MODEST
+Trace / Download+
252 HP / 4 Def / 252 SpA
-Charge Beam / Thunderbolt / Tri Attack
-Ice Beam / Tri Attack
-Thunder Wave / Icy Wind
-Recover / Protect
Called the Red Mage because it does a little bit of everything: it hurts and it heals, it enfeebles and it enhances, and it's slashed to high hell. (Also I couldn't think of anything "appropriate" like Standard, Special, etc.) Thunder Wave something or a couple somethings, Ice Beam what you can, Charge Beam what Ice Beam doesn't hit or what is too strong at the moment to beat, and Recover off the damage when you are able.
Icy Wind is another option if you have teammates fast enough to beat out the opposition when the foes are at 2/3 of their normal Spe. It hits both foes (most of the time) and has no type immunities, but it doesn't reduce Spe by a whole ton or stop the foes from attacking 25% of the time.
Trace and Download are both coin flip abilities, both in who they select and what they give you. It's hard to make a judgment on such things. If Download targets a SpD-weak Pokemon, you'll have over 250 SpA at once without having to Charge Beam, and if you Trace Intimidate or Swift Swim, you can really change the game. Generally I prefer Download, but Trace is still useful and not to be forgotten.
Tri Attack is included to not be walled by Lanturn and provide a stronger STAB attack, but prepare to be walled by other things with the loss of coverage, unless you want to lose one of Porygon 2's status-category moves.
The EVs are, as usual for the super-general GBU, very unspecific. If you want to make the most out of the Eviolite, you can split the SpA EVs between the defenses, or, if you're just out to KO the 4x Ice-weak-Dragons and Gyarados, you can find the SpA investment needed to KO them both with your offensive moves.
->Trick Room<-
Porygon 2 @ Eviolite
QUIET
+Download+
252 HP / 4 Def / 252 SpA
-Trick Room
-Ice Beam / Tri Attack
-Thunderbolt / Tri Attack
-Magic Coat / Protect
Download is chosen here because, if the two abilities were roughly equal before, Download edges out Trace a bit because of the presence of Swift Swim often in tandem with Politoed on Drizzle teams (If you want to hope for Inner Focus or something else, though, it may be to your benefit to keep Trace).
Here Thunder Wave and Icy Wind are sacrificed for the Trick Room spot, although they wouldn't be useful in TR anyway. The coverage moves are about the same, with Tri Attack in the background in case you don't need general coverage and want a stronger attack. Thunerbolt is chosen over Charge Beam this time because Porygon 2 plays a less stallish role, tending to want to hit hard while it can, and if it can't, disappear until Trick Room is necessary again.
Magic Coat is chosen here because it guards against Taunt, Sleep, and a turn 2 Encore from Whimsicott if the foe thinks you're going to stay in against it. Protect is chosen above Recover because of the same reason as Thunderbolt; Porygon 2 isn't (necessarily) playing in a Drought or Drizzle team, where, against many opponents, the effect will never end. Trick Room is inherently limited, and Porygon 2 doesn't want to fool around trying to win a war of being hit then recovering; Protect is preferred in this scenario because it tends to serve the one-turn purpose of stopping one attack while your partner deals with the other foe.