So hey, I'm building a dark type team for a in-game gym, and I wouldn't mind you giving your opinion on what to do.

My current team is as follows:

Absol (will not change)
Moves: psyco cut, night slash, thunderbolt, and shadow claw. (I play all out offense with my move sets and don't like to dabble in raising stats often)
Ability: super luck
Held item: absolite

Houndoom
Move set: beat up, smog, thunder fang, and flamethrower. (Thunder fang is simply for water type coverage, if you were wondering.)
Ability: flash fire
Item: black glasses. (Explanation: a houndoom looks beast in some shades and its main use is for boosting beat ups power)

These are the only two i have planned out. I plan on adding others such as cacturn, sharpedo, mightyena, honchkrow (the head honcho of all bird pokemon), ect. I just need to slimmer down my possible roster a bit.

Anyways, feel free to recommend anything that might help. I do not use legendaries, so please do not recommend those for my roster. Oh, and thanks for your time!

In the case of both Absol and Houndoom, you're splitting your offensive EVs, and both pokemon are closer to sweepers than walls... so with that in mind here are some suggestions to swap their moves around...
(The EV suggestions I've given here are just a very rough guide... I'm no expert in this stuff!)

Mega Absol (Attack)
EVs: 252 Att, 252 Sp, 4 Hp
Moves: Psycho cut, Night slash, Shadow claw, and Play Rough (egg move)
- You've stated you prefer an all out offensive, rather than setting up too much, so I gather you'd prefer wide coverage.  Play Rough hits hard, and has the advantage of sometimes reducing your opponent's attack - since absol has poor defenses, if you get lucky this could help you survive a little longer.
- Other considerations would be Protect/Detect and Megahorn (another egg move)
- Given your ability in your mega form (Magic Bounce), you might consider Sucker Punch instead of Night slash (or as an alternative 4th move) since your opponents are more likely to just attack you straight out (unless their raising stats) and this way you'll have priority.

Houndoom (Special Attack)
EVs: 252 SpA, 252 Sp, 4 SpD
Moves: Flamethrower, Sunny Day, Solar Beam (much better water coverage!) and Sludge Bomb
- Smog is incredibly weak, Sludge bomb is a direct upgrade to it.
- If you use Sunny Day, you weaken water opponents, clear up a pesky sandstorm from ground opponents, and get a single turn solar-beam to take them out... plus your flame thrower will be stronger too!
- Another option that I've found useful for Houndoom is Rest with a chesto berry as your held item - it's basically a full restore.

Your two chosen teammates so far are a physical and a special sweeper... so you might want to consider your defenses next... particularly your obvious dark-type defenses... Obviously Houndoom will be effective against bug-type opponents, but what about Fighting and Fairies?
Honchkrow, Mandibuzz and Malamar have type advantage against fighting, and skuntank, drapion and bisharp are good against fairies.

I know Honchkrow is the king of birds... but Mandibuzz is one beefy queen.  With a solid 110 hp, 105 def and 95 Sdef, plus access to roost and 2 decent defensive abilities, she can take a hit and keep on coming.  She might not be the hardest hitter, but she has some decent moves.
Since you're not one for setting up, perhaps consider something like...
Item: Leftovers
EVs: 252 Hp, 152 Def, 104 SpD (or any rough split between your defensive stats)
Moves: Roost, Fly/Bravebird, Steel Wing, Foul Play
Ability: Big Pecks/Overcoat
- Fly and Bravebird are both powerful, and leftovers will either give you a free turn of healing, or will help heal the damage you take.
- Steel wing gives some extra coverage with a small chance to raise defense (if you run up against entry hazard teams, consider defog instead)
- Roost is a decent go-to heal.  Just remember that it grounds you for one turn (so you can be hit by earthquake)
- Foul Play is a strong move that uses your opponent's physical stat instead of yours, so send Mandibuzz out to battle their physical sweeper, and she'll turn his own strength against him!

Aaaand a fairy counter for your team... As I said above skuntank and drapion could be good... but Bisharp's one of my favourite pokemon, so here's Bisharp:
EVs: 252 Att, 252 Def, 4 SpD
Ability: Defiant (this will make your enemy think twice about lowering your stats!)
Moves: Sucker Punch, Iron Head... aaaand take your pick - normally I'd go with Iron Defense/Swords Dance/Rock Polish (depending on EV setup) and Toxic/Stealth Rock, but you could choose Psycho Cut/Poison Jab/X-Scissor for coverage or Torment to potentially trick your opponent into increasing your attack via Defiant.
- As I mentioned with Absol, Sucker Punch gives you a strong STAB-priority move, as long as you can anticipate when they'll attack (this is why I didn't include EVs in speed).
- Your ability makes your opponent think twice about defogging (or aegislash swapping back to defensive stance), lest they give you an attack boost.
- Iron head gives you STAB coverage and helps your team fight fairies.

Let me know if you like any of these suggestions and I can help you work on the rest of your team.  Dark pokemon are my favourite, so I love looking at what they can do.

Oh dear god mandibuzz is a dark type? Ugh... Id totally use it if it didn't look so... Ugly. I just dont like the design. Its odd, and, although relevant to its original real life version, the vulture, it's just disturbing to me and... Just... Ugh, i dont like it. But it is a good set up you have, dont get me wrong.

As for bisharp, I would love to use it in my team. Its design is cool and pretty original, has a dark type vibe to it, and its stats are pretty good. I remember running this guy in white version, it was a good time me and bisharp shared together. Alas, the game got stale after beating the elite four, and whats worse, i lost the game a week after completion. *sigh* ;-; but yeah, I'll see what else bisharp can learn and I'll select something for his last two moves, such as grass knot for pesky ground/rock types and dig for fire types.

I agree with you about mandibuzz - she just doesn't look so cool when you compare her with Honchkrow.  She is a great tank, though, so if you put your team together and find it isn't working as well as you'd hoped, consider giving her a go.

As for Grass Knot on Bisharp, while the opponents weight does determine the base power of this move, it's still a special move and will use your special attack stat to determine final damage.  Unless you're up against a Golem or something (when grass knot has 120 base power and 4x damage due to typing), you'll get a lot more out of a move that uses the attack stat instead.
Dig could work, although that turn below ground gives your opponent a chance to set up or take you out with Earthquake.  Try Psycho Cut, Poison Jab, X-Scissor, Shadow Claw or Brick Break.  If you feel lucky you could consider Stone Edge, which is very strong but only 80% accurate (I personally feel that's too low, but your mileage may vary).
It might be easier to work out the rest of your team and come back to Bisharp - you might find the choice is obvious if nobody else covers a particular type that Bisharp can.

As for other dark pokemon, here are some fully evolved non-mega, non-legendary pokemon that could be viable based on stats and other abilities...
- Umbreon (like Mandibuzz, it has tank based stats... it's not quite as good as the vulture, but you could get some mileage from Moonlight, Confuse Ray, Dark Pulse and perhaps Shadow Ball)
- Tyranitar, the stat god of dark pokemon (Earthquake's a given, and consider Crunch, and either Stealth Rock and Dragon Tail (a very mean combination) or any combination of Outrage, Dragon Dance, Dragon Tail (to send pesky fighting pokemon back to their trainer) and Rock Slide/Stone Edge.
- Sableye with Prankster can be pretty good, but requires a lot of status moves which you're not keen on (Confuse Ray, Toxic, Substitute and Moonlight could be a good sableye set)
- Sharpedo with Speed Boost and Night Slash, Waterfall, Earthquake and Aqua Jet could be a decent speedy sweeper (but it's a glass cannon, and it's speed won't compare with a lot of others)
- Cacturne could be a physical or a special attacker, and if you're allowed Sand Veil, he could take advantage of Tyranitar's sand.
- Crawdaunt with Adaptablitily and Crabhammer, Crunch, Nightslash (and one other) will be a hard hitting beast
- Honchkrow can be decent (but not great) with Roost, Brave Bird/Fly, Night Slash/Foul Play/Sucker Punch... it's not great, but he can do some damage.
- Skuntank, like Honchkrow, relies on a few status moves to really be effective.
- Spiritomb's also a big status-user.
- Drapion with Sniper and as many high-crit moves as you can get would be good - Cross Poison, Night Slash... and any 2 moves to help keep you alive, or perhaps Infestation, to keep them from swapping before you take them out.  With Sniper you should only really be attacking with Night Slash or Cross Poison, so I wouldn't worry about coverage.
- Weavile is a good glass cannon - give it Icicle Crash and Night Slash, and pick whatever else you want, just stay well away from special moves.
- Krookodile's pretty strong and can work with a similar move set to Tyranitar - while not quite as powerful, you do get STAB earthquakes, and you might be able to take one hit from a fighting type before fainting.
- Scrafty's quite bulky and has some pretty cool ability choices.  Perhaps Hi-Jump Kick, Fire Punch, Drain Punch and Rock Tomb/Head Smash for birds.
- Zoroark's powerful, but it's main advantage using Illusion to play mind games.  On an all-dark team that won't work very well, so unless you really like it, I'd go for something else that you can make good use of.
- Hydreigon.  This guy is a special attacker, which most other dark types aren't.  Just don't let him go up against a fairy.  Take Draco Meteor, and pick whatever will help you get decent type coverage for your team.  Charge Beam is weak, but it does allow you to attack and power up for other attacks at the same time, so you might find it worth while.  Otherwise you have Earth Power, Surf, Flash Cannon, Flame Thrower/Fire Blast, Focus Blast...
- Greninja with Protean is amazing - you change your typing to give your attacks STAB, and change your weaknesses (which can keep your enemy guessing).  Take whichever special attacks you need to cover your team.  Extrasensory, Ice Beam, Grass Knot, Scald, for example.
- Pangoro with Iron Fist would have a powerful Hammer Arm.  He doesn't have most of the other moves that would benefit from that ability though.  Still worth a look.
- Malamar is a bit of a niche pokemon - with Contrary and Superpower you have a massively powerful attack that also makes you stronger, and it's complimented well by things like trick room and topsy turvy, but you prefer basic offense, so Malamar probably isn't for you.

Hopefully list list helps you narrow down what you'd like.  I'd probably suggest Greninja and perhaps Scrafty or Drapion, and whichever third you like most.

I'm definitely taking tyranitar, and hydreigon will be an accept ion because, although i don't really like his final evolution design, it is a complete boss with special attack. Besides, bisharp will be able to take care of any fairy type pokémon i have to face. The only problem i see is raising them. XD i don't have a Black/white game anymore, and I'm not quite sure on where to find a Puritar/larvitar for training. Besides, pupitar will be a pain leveling up. Cacturn is good, because i didn't really want to use shiftry due to the fact he kinda annoyed me in the mystery dungeon games. ._.

Greninja shouldn't be hard to do, seeing as froakies are everywhere around the world of wonder trade.

Thanks! I really appreciate you taking the time out of your schedule to help me out with this, honest! I wish i could repay you but I'm not sure on how to XD

Pupitar can be found in the friend safari from people with a rock-type safari. I think I actually give pupitar in my safari, if you need it.
Zweilous can be found in Victory road (I don't think you can get it from friend safari, might be wrong though).
You really need greninja's hidden ability for it to be worthwhile, so make sure it has Protean.

You don't have to repay me, I enjoy this stuff!

But I feel the urge to repay you! -3- im a repay zombie. Muuuussstt.... Repay favoooorrr.... Oh and brains but mostly repay favorrrr....

I'll need to look up hidden abilities then... I'm not really sure on how to get them.

Yes please! Whats your friend code?

In X and Y you can get hidden abilities in 2 ways:
- Pokemon from hoard battles have a 20% (1/5) chance to have their hidden ability.
- Pokemon in the friend safari have their hidden ability if you're playing at the same time as the friend who's safari you're in is playing (I don't know what the chance is for this one, I think it's 50%)

My FC is 3110-3930-6403

Thanks. I'll grab a bird pokemans and fly on over to my friend safari.

Ya know i could do a overworld sprite for you. Only one frame, but I'm pretty good/decent at them if ya ask me. Just give me a idea of what you want and I'll see what I can do!

You'll have to give me your fc too or you can't access my safari.
I'm honestly not sure what I'd want on a sprite yet, but if I think of something I'll let you know, thanks.

I'm aware of that. XD give me a second...

No problem. :3

1934-1423-1330

Sorry for the delay, just added you now.