Hello Everyone, i'd just like to say that this is my first guide attempt and i hope you find it informative.

In my experience i find Blitz isnt a spectacular tank but he is somewhat tanky.
He can be played several ways so he is a good choice for a blind pick match.
His versatility includes as/ad, ap/tank, crit/ad, and crit/as and probably more good choices.
This guide focuses on as/ad more than anything with a bit of a tank hybrid quality.
I find a good blitz build is perfect for a lifesteal carry (unlike many champions who just use lifesteal without good reason).

My item choice probably seems a bit odd to some but i had team fighting in mind along with 1v1 capability and early game versatility.

Heart of Gold - i get this early on to help with Blitz survivability and overall gold accumulation (which for this build it is very expensive). It's also good to have to help reduce the cost of randuin's omen.

Ninja Tabi - Since the Sejuani patch the 10% reduced basic attack damage reduction comes in handy for surviving and jungling early game. Eventually you will be getting rid of this exquisite item in order to make room for a blackened cleaver.

Glacial Shroud - by now it's likely mid game or if you have been getting fed still early in which case this item will give you some much needed armor, mana (desperatly needed), and cooldown reduction (for that long wait after using rocket grab).

Phage - by now it's mid game and most likely people will start ganking so why not join 'em.
As a piece of frozen mallet your getting this like it or not but since you are why not get some use of it while everyone isn't yet engaged in team fights.

Emblem of Valour - a piece of stark's fervor with much appretiated lifesteal, after you get this jungling is a cinch.

Giant's Belt - Another piece of frozen mallet and a nice item for hp. I get it just so i can have a full 6 items and get frozen mallet sooner.

Now for the final items with in-depth explanations for each one

Frozen Heart - Armor, mana and cooldown reduction. The aura makes most dps players hate you. I get this because Blitz' grab requires him to take a few hits afterward (naturally) and it helps you kill ranged dps champs much easier.

Frozen Mallet - Hp, ad and on hit slow by 40%. I get this to ensure myself or my allies are able to get kills as well as a nice hp boost. Since in the end i sell my boots im in need for compensation of 70 move speed (though with rank 5 overdrive your move speed becomes 390 anyway), this helps enormously to catch and kill runners. FM also makes it easier to land your grab and more chances to use Power Fist. Needless to say a solo target probably isnt getting away from you and your team.

Stark's Fervor - a magnificent item that gives you and your allies an aura. Since my Blitz build focuses on hp, ad and as this item is almost essential plus assuming 1 other ally gets one that adds up to 40% lifesteal, 60% as and 40 armor pen. with my build fully exploited my ad was at 302, lifesteal totaling at 65%, 251 armor, over 3500 hp and over 2.0 as i was a very difficult to kill Blitz even when focused (the Mobafire stat calculator at level 18 doesn't account for everything).

Blood Thirster - A favorite for any dps and of mine as well. The raw ad and lifesteal make it an excellent choice and changes you from a simple disabler into a carry. B-thirster is essential to this build and makes you much more versatile. I find lifesteal isnt worthwhile unless your champions has decent of the following stats: ad, hp, as, above 50% lifesteal and armor/magic resist (which is extremely difficult to find a decent balance of said stats).

Blackened Cleaver - if you get this far i commend you highly. This item gives you the iceing on the cake, so to speak. Additional ad, as and that armor pen on hit effect that changes tanky carries into simple carries. BC makes most champions Blitz grabs barely able to fight back considering his W, E, R, frozen heart and randuin's omen combo.

Randuin's Omen - an uncredited item in my opinion. Hp, amror and that chance to slow enemy as and move speed, whenever i get this far in the build the enemy team usually targets me first in team fights which is their own downfall. The combined FH slow along with RO slow make enemy teams 55% slower attacking speeds should they choose to target you. It is especially effective when chasing champions with on hit slows from abilities or items like frozen mallet as they will usually hit you to slow but risk slowing themselves as well.

All these items tie in wonderfully with Blitz' abilities and somewhat hard to kill nature.

The reason for getting rid of my boots should the battle rage on long enough for you to afford everything getting rid of your boots is usually a smart tactic to give you an edge over players who keep their boots. it is not advised for champions who dont have additional movement speed abilities, however unless you use ghostwalk wisely.

pro - early and mid game tanky is ideal for preventing your lane from feeding. Everyone knows if you feed them early they just get more and more fed as the game progresses.

pro - mana ceases to be a problem after frozen heart.

pro- Blitz uses his W to gain move speed and attack speed which makes his boots unnecessary during late game and enables him to hit above 2.0 attack speed with this build + surge.

pro - can grab a single enemy champion from a distance allowing you to 1v1 them and get the kill before reinforcements arrive. This build allows you to take the hits during a 1v1 as well as get the kill and completely disallow them from escaping due to frozen mallet. After you should also be healthy enough to rejoin the team fight.

pro - Lifesteal + decent damage + semi-high hp + tankyness = one of the most ideal champions to have lifesteal with because you will be able to survive long enough to gain your hp back before you die. I cannot stress how well lifesteal works with this build, allowing you to succeed a 1v2 assuming they arent ap carries.

pro - this build will likely have the enemy team focus you in team fights because of your disable abilities and items. Your frozen heart and randuin's Omen will slow them making them easier targets for your allies.

con - this build is rather expensive and can take a long time to farm for, most matches will end before you finish your bloodthirster.

con - with the eventual loss of mobility you cannot escape nearly as easily as you would normally.

con - you have a huge weakness, and thats magic damage. MD destroys you if you arent able to close the gap quickly enough or even if they enemy is too tanky to kill quickly.

con - this build may sustain you for a longer time than a carry but your damage output wont be nearly as high so even if an enemy cant escape you easily reinforcements may be able to assist your target.

con - you are not the initiator unless you can land your grab so dont run in their and get yourself killed.

con - this build will likely have the enemy team focus you in team fights because of your disable abilities and items.

I choose 9/21/0 because it helps blitz get that extra boost of survivability he may or may not need in early and mid game and also when late game comes around you get your attacking items which helps make you a devastating hybrid.

There is only 1 item Blitz gets for armor pen which is blackened cleaver so the offensive mastery which grants 10% armor pen is almost essential.

runes are flat attack speed which may feel unimportant until you get your attacking items but once you do you are able to hit very fast and usually overpower many other champions.

Exhaust is an amazing spell as isn't all that necessary for this build during late game but i take it because its great for early game escaping or killing.

I could recommend ghost walk instead for the speed boost and running through minions in order to line up a rocket grab more easily.
Teleport is another good choice if you focus on late game, because of the loss of your boots you become slower and unable to get to where you need to be at times.

Surge is not absolutely essential either but makes it much easier to get kills in mid game and makes you attack considerably faster at late game which helps to single out a target quicker. Surge cannot be used defensively, however.

Teleport and Ghost walk are excellent choices to replace Surge. As per usual Flash is probably one of the best choices to go with because of it's offensive and defensive capabilities but i find blitz is fast enough and his disables are quite excellent in order to chase or escape enemies. Along with frozen mallet escaping becomes quite a bit easier and because of his grab you may even be able to pull someone back to you who had used Flash to get away. To stop someone who uses Flash to chase you you will probably always have your E to pop them into the air giving them a slow from FM and the means to escape.

I have always thought of Blitz as a overpowered disabler which is why he goes so well with frozen heart, frozen mallet and Randuin's Omen. He can slow an entire team and survive long enough for your teammates to do some serious damage, even if you do take the fall it usually isn't in vain. Often i run into an entire team in the brush and they usually burst me with everything they have, I usually survive the initial burst or slows and exhausts and stuns and immense damage only to narrowly escape with a shred of hp left which allows the rest of my team to make quick work of them because i was able to absorb everything and survive. Stark's fervor is great to have too because being somewhat tanky it gets plenty of use by other ad carries, they will love you for it. I have tested this out against Jarvan, Sejuani, Malphite and Blitz tanks (1v1 mind you) with full builds and am often able to kill them without trouble of them escaping. On average this build yeilds over 15/less than 10/over 20 (kill/death/assist) ratios as well as 200k damage dealt and over 100k damage recieved during a match lasting over 50 minutes.