Tank You Omniknight

Items?

Pretty standard stuff here. As the secondary support, you get to spend a portion of your starting gold for the good of the team! Grab chicken or wards, whichever is left to get. Also, note that I don't have anything in the guide about you buying a steady stream of wards. Unless your main support is out of gold, or until you finish your core items, leave this to them. After that, it's good to let them catch up on their farm as well.

Orb of Venom and one level in Degen Aura work well together to keep a enemy in kill range if your team can get you in melee range. I also find that the extra level that you would have in repel does a lot less for you in a dive than the slow does. I don't get more levels early on because one is enough to keep most heroes close enough to Orb of Venom them in the face.

Note: if your carry is going Drums, then you can just build a Bracer and be fine.

I prefer treads because of the hp or mana it can give you in a pinch. The attack speed is negligible on omni but the swing-able ten stats are nice. Everyone has different options on boots; in this case, go after what you like.

Why pipe over mek? Well, for starters, I like to spread out the heals that can come out of our team; if I get pinned, I would really like our other support to give me a little Mek love. This works the other way as well around as well. Pipe synergies with ult perfectly, makes you even more tank, and ensures you get the pipe charge off in a fight.
That being said, if for some reason SUPPORT HERO X doesn't get the mek, it is better for that you pick up both than to go without.

The rest of the items are pretty standard. I don't do Radiance because, with that much farm on Omni, your carry should have a complete build, so the burn wouldn't be noticed anyway. I prefer Halberd to Heart because of its useful ability and the evasion being worth more than the straight HP.

Why Omni

Well lets try to start this off by making everyone rage. Omni is not a hard support, if you are looking for a hero you to support your team with there are much better pick ups so you should probable find a different hero. Now that being said Omni is a great support hero in lane and team-fights, but he doesn't have the aggressive move set and item independence that you need with a hard support. If your taking last hits from your carry, or if the enemy team is able to keep harassment on your carry then you aren't doing your job as a support. Winning a lane isn't about not dying or getting kills, its about denying farm and experience to your opponent while keeping your carries farm at a decent stream. Omni is one of the most situation picks in the game, but when the all stars and moons aline and he is the right hero for the job, you should know how to play him.

Pros / Cons

Early Game

Grab your items, (if your team already has a chicken get some wards for the long lane) and head to lane. When picking your lane as omni you need to have someone with a disable to get you in close. If this means that your tri-laning or if your running the 2-1-2 head to where your going to be helpful. If your team doesn't pick a hard support or the other support doesn't want to help, then you should try for a full support build in one of the other guides.

In a defensive tri-lane you want to position yourself along the tree line out side of the lane. Stay close enough for xp but if your teammates aren't ready to go in be quick to pull and stack your camp as this is going to be your main source of gold and xp. After you stack the camp, you can pull it into lane and kill off your own wave. In a tri-lane you don't try to keep the neutrals at full health. The key is to try to have them all die at about the same time and to get a large amount of the last hits. Try to stay close enough to get back in lane if your opponent over extends or your disabler gets a good stun in.
Get a tp early, if the other team is diving a different lane you are the best one to stop it.

If your in a offensive tri-lane stay in lane as close in as you can get without drawing auto attack harassment. you really need to look for your farm in these lanes and if you pressure and get kills early you won't fall behind. Luckily Omni can dive better than almost any hero in dota, run in and tank while your disable gets in there to pin them down. If you can hold the heal to damage that's great but don't die in a dive. If your in deep and it starts to fall apart run strait thru and loop back past the trees. This will save you the extra damage you will get from stopping and turning. Good offensive warding is a major key to winning this lane.

If you are running a dual lane don't go with the carry. You can't afford to take his farm and you need items to be able to function. It is easy for Omni to run in the hard lane since he his so hard to take down and he does a fair job of getting others out as well. Don't die for your teammates at this stage of the game. You need gold and xp from being in lane as much as they do. Keep that tp scroll on you and feel free to tp in and tank for a gank under towers if your needed.

Out of the laning phase and into the teamfights.

If your team wasn't planning on big team pushes then they wouldn't have picked Omni up. Once you get up a decent amount of tank, stay to the front of the push and make yourself a tasty target. The enemy will want and need to take you down before they make a real effort to stop your team. Don't ult for just yourself, if it looks like your team is out of postion after they start to swarm you down, tell them to back down and go down like a man (heal, repel, and run like hell.) But when you do hit that good ult, get in on your target and stay with them. If you die once your ult, heal, pipe, and repel are out then you still managed to do your job. I can not stress enough that repel is not a replacement for BKB on your carry. They should have been able to farm a BKB by this point in the game and in many ways it superior to your repel. If they do have their BKB repel the person that will make the most of the team fight. Batrider or Jakiro will dominate fights if no one can pin them down, but they usually don't go for BKB in their builds.

Omniknights Blackbook

I guess I should start out by saying everything in Dota is situational. Don't force something that doesn't fit.

Be careful picking Omniknight against the following heroes.
Doom- He can turn you into a really fancy creep with his ult. He doesn't counter you but he will be looking to ult you all game long.
Invoker- Tornado and EMP= worthless omni. Tornado will purge off your ult (this applies to euls as well) and EMP will destroy your ever fragile mana pool.
Anti-Mage- His mana burn will be rough on you as your pool is low and you need every point of mana you have. Repel stops the burn btw.
Naga-can waste your ult and pipe with one good ult. Repel also keeps you from sleeping so she can pick off who ever your trying to save (note this works with her on you team if you repel an enemy as well). Net is boss against magic Immune and most Naga's will pick up mana burn at some point.
Rubick- With great ults comes great chances Rubick will steal that ult. His move set is much better than yours so Omni ult is pretty serious on him.

Euls, Diffusal, and Necro book are also big counters to Omni so pay close attention to what the enemy team is getting to counter you.

Tucking It In

Will be happy to answer any questions about the build or if I have time to show new players tricks they can use to improve their game play. Be nice with your post, I am not here to tell you this is the way you have to play omni, just this is the way i play omni. I will make it fancier as I go along this is just the start of the guide.