Hey guys! As a part of revising this guide extensively to reflect the new meta, and with a better appreciation of what Heimer is, I'm rewriting the intro (and most of the rest of the guide).

What is Heimer? I will tell you what he is not. HEIMER IS NOT A CARRY. He is a great champ, but you have to understand what he has to offer.

{SEASON 3 UPDATE IN PROGRESS 12/18/12} I'm re-writing this guide for the new itemization and also reflecting more experience in ranked with Heimer.

Marks: Flat Magic Resist
Seals: Flat Mana Regen
Glyphs: Flat AP
Quints: Flat AP

As a side note, magic pen does not help your turrets, I've tested it more than once in custom games. The aura from the Abyssal Scepter is the exception to this, so consider getting it if you want to pursue a more turret-oriented route. That's a decent item for Heimer, but a late game one.

The Blackfire Torch is really great, and makes Heimer much more viable overall. You can grab Kage's Lucky Pick early on and benefit from the GP/5 while you build it. The fire damage from Blackfire Torch juices up your rockets nicely, and seems to apply the effect to every target you hit. Too bad it's only in Dominion.

If you have sustain issues in lane, you can try picking up a Philo stone first. It's rare to totally finish your build, so you can hold onto the Philo stone pretty much all game.

Building the Needlessly Large Rod next - you have some time to consider whether to pick up Rabadon's or the Hourglass. If the game goes on long enough, you'll want both. If the game goes on that long, however, you're going to have bigger problems, as Heimer becomes progressively less competitive the longer the game goes on.

The priority order goes
Upgrade!!! > Rockets > Turrets> Grenade

Take your turret at level one, and use it as a ward. They have an attack speed bonus when you first lay them, so basically always want to have them queue'd up for use in a fight. Turret damage is sad enough without handicapping yourself by setting them up before a fight and wasting that AS bonus.

You should pick up grenade at level 3, and then prioritize rockets after that. If you're laning against someone aggressive, it's nice to plant the 'nade on their forehead when they rush in at you. Given Heimer's slow run speed, you will occasionally need both the nade stun and your flash to escape a gank.

If you're dealing with someone like Xin or Irelia, you can choose to level up the nade first. The blind on the grenade is one of the most underrated abilities in the game, in my opinion. If you're up against an AP carry, level turrets over grenades, as the stun never gets any longer on the nade, only the blind.

Note: Some people recommend only taking rank 1 of your ult instead of taking the following ranks whenever they're available. I like the CD reduction on the ult, so I take it at the normal levels. Once you get good at juking, kiting through your ulted turrets, etc. you will survive to use your abilities more than once, even against tough customers. CD reduction helps you win.

Barrier
Flash

You can take Ghost instead of Barrier, but I don't recommend it. Half the time you'll be slowed anyways, reducing the utility of ghost. Barrier really makes the difference in those early and mid-game fights.

I also don't recommend Ignite, as it's mostly the tool of champs with big burst. Heimer really can only burst champions who jump on your face expecting you to fall over dead as soon as they do. The rest of the time he harasses the enemy until they have a permanent rocket imprint on their forehead.

Okay, now to the fun stuff!

Levels 1-4:
Alright, so your first point goes into turrets. You'll want to lay this in the river bush to act as a free ward. You keep turrets at level one for awhile, simply because ranking up turrets does not improve their damage, with the exception of rank 3 when you can place two. Also your turrets get an attack speed bonus for the first few seconds after you lay them, so it's usually best to drop one as a fight starts rather than pre-positioning it.

Rockets do piddly damage at rank 1, but they start stinging a bit at rank 2 and get better from there. Use them to last hit multiple mobs at a time and to harass the enemy champs. If the enemy closes with you, drop your turret (you should always have one ready to go since your turret has been sitting in the river bush keeping you safe). Turrets auto-target enemy champs when first dropped, so in general enemies have to back off until your turret swaps to creeps.

Always understand that Heimer is a poker, not a nuker. Harass the dickens out of the enemy and force them to B. Avoid overextending yourself for a kill - most times you'll be the one dead.

Levels 5-9:

This is a good time for Heimer. Your rockets start doing solid damage around level 5. Concentrate on farming and harassing. If you've warded yourself well (and you have Flash up), you can probably start pushing into their tower and applying more pressure.

Levels 10-18:

Your rockets max out at level 9, at this point Heimer is close to his peak and it's important to make the most of it. Leave your turret to keep a lane pushed up and roam. Plant wards in the enemy jungle, gank the other lanes, wreak havoc any way you can. You can land long range 'nades fairly often if they don't see you coming.

Team fighting as Heimer is all about positioning (no ****, you say). You have to take some level of risk when placing your turrets, but of course you can easily be stomped on while you place them. There are a few tricks to help ease this difficulty, but in the end it's just part of the game.

Heimer's big addition to the team is his grenade. Rockets do nice damage, and turrets can be useful in games where the enemy doesn't have much AOE, but the AOE blind from the grenade is a game changer when used correctly. Your best use for the grenade is blinding someone like Xin for 3 seconds, but if he's not around you can drop it on the enemy carry's head to allow your teammates to catch up and crush them.

As Heimer you should constantly be moving around the map, taking advantage of your turrets. Go to an empty lane, drop your turret where the creeps are fighting each other, and then go elsewhere. In this manner you can push multiple lanes and continue farming (you get exp and gold if your turrets last hit, even when you're not in the area) with almost no risk.

General Thoughts on Gameplay

Okay, so let's talk frankly. Your ult is essentially a half-*** slow and some CD reduction. That leaves turrets, rockets, and the grenade. Fortunately, that's all Heimer needs to frustrate the hell out of the enemy.

Rockets you use early and often. Depending on your team comp the enemy may not have built much magic resist, in which case your damage actually scales pretty well into end game, but versus beefy champs like Malph or Singed, you'll basically need both turrets, repeated rockets, at least one well placed grenade, and hopefully a turret or some creeps to help you out. Sorry, that's just how it goes. As Heimer, if you're in a fair fight you've already done something wrong.

Additional Comments
-The mark of a bad Heimer is when he lobs long range grenades to try and get damage on someone (unless you have blue buff, and sometimes even then). Use rockets only for harass until the range is short enough that you're sure to land the grenade stun. Against champs like Xin, Irelia, etc. always ALWAYS save grenade until after they use their charge. Same goes for AD carries like Vayne - try to wait until she rolls in, and then toss your grenade. Use bushes a lot, when people chase you in you know where they're going to be and you can nail the grenade stun much more easily.
-Keep an eye on turrets you have down even when you're shopping or in other lanes. You will occasionally have an opportunity to help a teammate out by ulting, putting the slow on the enemy.
-Barrier and Flash are, in my opinion, essential summoner spells because Heimer is slow and squishy, but you need a fairly scrappy playstyle to get the most out of your grenades. Flash is also nice offensively, for turret placement and better rocket control.
-The map is Heimer's best friend. The long range on rockets (and short effective range of your grenade) means you need to play ring around the rosie games with enemy champs whenever possible. Set up ambushes in bushes, kite around turrets when enemy heavies are diving you... in general you want to be a hard-nosed stubborn bastard who just will not go down. You are not Mike Tyson. You will not destroy people just by running through your abilities one time, like some AP champs I could name. You are Muhammed Ali. The game is attrition. Practice it.