First Competitive Fully EV Trained Team

Timid Espeon @ Light Clay
252 HP / 4 Def / 252 Spe
Magic Bounce
Reflect
Psychic
Baton Pass
Light Sceen

Jolly Gliscor @ Toxic Orb
252 HP / 40 Def / 216 Spe
Poison Heal
Toxic
Protect
Substitute
Earthquake

Impish Dusknoir @ Leftovers
252 HP / 28 Atk / 228 Def
Pressure
Pain Split
Ice Punch
Earthquake
Will-O-Wisp

Timid Darkrai @ Leftovers
4 HP / 252 SpA / 252 Spe
Bad Dreams
Dark Void
Nasty Plot
Dark Pulse
Focus Blast

Modest Volcarona @ Chesto Berry
160 HP / 252 SpA / 96 Spe
Flame Body
Rest
Bug Buzz
Fiery Dance
Quiver Dance

Naive Meloetta-A&P @ Normal Gem
56 Atk / 252 SpA / 200 Spe
Serene Grace
Psychic
Acrobatics
Relic Song
Close Combat

Well, after a many an hour of investment, I finally have, what I would like to think of as a "decent" competitive team... I only recently looked into the mechanics behind EV's, and this is my first team making use of them. I was hoping that some of my battle-seasoned sempai's could give me some constructive criticism ^^'

While Dusknoir has high defenses and a good offensive move pool, Dusclops outclasses it defensively due to Eviolite and Gengar outclasses it offensively. I'd use Gengar if I were you:
-Substitute
-Disable/Pain Split/Thunderbolt/Hidden Power (Fire)
-Shadow Ball
-Focus Blast
Nature: Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Black Sludge/Life Orb

Or
-Protect
-Shadow Ball
-Focus Blast
-Hidden Power (Fire)
Nature: Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Life Orb

Gliscor's current set is better off using a defensive spread to take advantage of Gliscor's high Defense: Impish with 248 HP/24 Def/236 Spe

Darkrai is an Über Pokemon so it can't be used in OU teams. IMO, Ferrothorn would be useful for hazard support:
-Stealth Rock/Spikes
-Leech Seed
-Power Whip/Protect
-Gyro Ball/Thunder Wave/Protect
Nature: Relaxed
EVs: 252 HP/88 Def/168 SDef
Item: Leftovers/Shed Shell

While Meloetta is rather unpredictable because of Relic Song, it makes half your team weak to Darks and Ghosts. Infernape has its own degree of unpredictability:
-Overheat/Fire Blast
-Close Combat
-Grass Knot/U-turn
-Stone Edge/ Mach Punch
Nature: Hasty/Naive
EVs: 252 Atk/4 SAtk/252 Spe
Item: Life Orb

Thank you, Platinum Dude. I'll look into that Gengar right away. As for Darkrai, are you refering to Smogon's Tier's? If I want to battle here, do I have to abide by those as well? ... And, assuming so, can Ferrothorn not learn Spikes AND Stealth Rock?

As for Meloetta... Well, I have to have at least one of my favorite Pokemon on my actual team ^^'

Yes, yes I was referring to Smogon's tiers. It might be a better idea to abide by Smogon's tiers just in case your opponent does too.

Also, if you do want to keep Meloetta, Gem + Acrobatics is done better by Archeops and Drifblim. It needs more coverage than just Acrobatics:
-Relic Song
-Close Combat
-Thunderbolt
-Psychic/Hidden Power (Ice)
Nature: Hasty/Naive
EVs: 56 Atk/252 SAtk/200 Spe
Item: Life Orb/Expert Belt

Now this, I could work with. Thank you ^^

But, what about stealth rock + spikes? Is that not allowed or frowned upon?

It's better to use 1 hazard because Ferrothorn lacks recovery outside of Leech Seed, Leftovers and Rest.