Are you genuinely interested in taking a Steelix deck to a tournament? If so, I'l write you a book, lol.
I won't pick at your list too much, but here are a few things I think need some work:
Onix:
Run the UL Onix with the CCC attack, its infinitely better. Harden is nice, but how many attack really do less than 40? And, it can't really attack as well. A belted UL Onix OHKO's Luxray with one heads and the belt keeps it just out of Crobat range, unless your opponent wants to waste 3 Flash Bites on 1 KO, I'll give it to then, even if it nets them 2 prizes.
Azelf/Unown Q:
I think both are uneeded. Attaching to Sableye and discarding to retreat helps dump energy into the discard. Azelf, while nice, isn't really needed. Don't get me wrong, about every third to fourth match, I'm always asking myself "Why don't I run Azelf!!!" But, at the end of the day, I'm always content that I don't as that would just be one more prize I would have to give up (Anythingchomp, ERL, Shadow Room)
Edit: To elaborate on this point a little: I had all but 1 Onix prized, both Blissey, and Uxie all in one game. I won, but I was scrambling, you can't REALLY prepare for that.
Pokemon Collector:
Since you are running Sableye, I think you can get away with just running 2 Collectors. Not a huge change, but lists get tight quick.
VS Seeker:
What a great card. But, you lose a lot of flexibility by running 4. First, it can be trainer locked and ruin your deck. But, if you run 1-2 and just take the other remaining spots and fill them up with the actual Supporters, you'll fair better. Another scenario I see happening is you get stuck with only one supporter in the Discard and can't meet the requirement to play it (don't have an energy for Engineer's, aren't behind, can't Twins, don't need a Poke search, you need a draw, you get the idea). But, I will say VS Seeker and Junk Arm is disgusting. I've judge 6 turns in a row and used twins 3 turns in a row (absolutely broken when paired with Jirachi RR).
Stadiums:
I think this deck MUST have stadiums. The best is Conductive Quarry. I used Ruins of Alph as a Luxray counter but I've found Plus Power and Junk Arm a much better combo. BTS just doesn't really work: rarely will you NEED to use it to evolve. The issue usually isn't evolving, its usually getting Steelix in your hand. Plus, he needs a lot of energy attached and energy in the Discard. Running only 2 BTS just isn't worth it as you will usually run into them late and already be set up but a late game Conductive Quarry helps tons. It also lets you lock up the Stadium war against Dialgachomp to avoid being Skuntank poisoned yourself.
Seeker:
3 Seeker seems like 3 seeker too many, lol. I tried running 2 once upon a time. Great in theory, but I've always found myself wishing I had played another supporter and it not really helping me as much as I thought.
Healing cards (Life Herb):
Life Herb paired with Junk Arm is another disgusting combo in this deck, too good to over look I think. I hate flippy cards, but running 4 of them, odds are you'll hit 2 and that's probably all you will really need. It also removes special conditions, helpful with Poisned against Dialga.
Judge:
I would run 6 of them in my list if I could. Blissey allows good recovery and running a thick line means your opponent will pay for using Smeargle.
Plus Power
Think of how many T1 decks fall JUST outside of Steelix's OHKO range, noteably DGX and Gyarados.
Call
I honestly believe this deck has to have a Call type of attack (call energy or call for family) to set up. Granted, you won't get it up T1 every time, but you will set up way more consistently. I recommend Call Energy and even a few Energy Exchangers.
Edit: I just remember you run Sableye with collectors. I run a Jirachi engine and don't play Collectors. Having said that, I think Sableye/Collector is almost as good, but I think running call energy would still help. Also, if you are going to run Sableye, I think it might be a good idea to try and squeeze in 1-2 Cyrus's to grab a Supporter and an energy.
Trainer Lock
Steelix fairs well against trainer lock, but you have to plan for it. First, Judges help a lot. Second, (obviously) ditch them early. With resistance to Gengar and the ability to OHKO and avoid fainting spell, you have a great shot. Another card that helps is Volkner. I used to be adamant about how much better Engineer's was until I started running a lot of judges. When you judge your hand to 4, you can ditch a trainer next turn with Blissey and another with Volkner and draw 4. In non trainer lock, paired with Junk Arm(discarding 2 plus Junk arm = 3 cards), Volkner is far superior.
I love Steelix. One of the first tings that drew me to it was the "play from the discard" idea. As with any deck, test, test, test, your results won't lie and they will tell you exactly what you need. When you get your list down pretty tight, Steelix is MEAN.
I'm going to try and squeeze in 1 Lost Remover when it comes out....can't wait.
