In this guide I will show you how to build AP-TANK Blitzcrank, which let you devastate your enemies and survive some gang attacks. You have to be tricky and use the environment to bring people down but remember you will not be so hard to hold out whole enemy team. Just focus the weakest and the strongest champion, pull him and destroy or let your team do that. They will be thankful they have you at their site. So if you want to make a havoc, got dozens of kills and win many of matches, just choose the Blitzcrank because... "The time of man has come to an end".

Advantages

- much of health
- low ultimate cooldown
- one of the great passive
- great to chase and escape
- can grab enemy through walls
- hard to kill
- flat mana cost of the skills

Disadvantages

- mana dependant early game
- no direct skills
- a bit useless without Rocket Grab and Static Filed
- high mana cost/cooldown of Rocket Grab

IGNITE

Very useful and helpful skill especially at the beginning. It helped me gain many kills in early game. However a bit useless in later game but still works great vs healing champions. I think it is worth to take it because early kills = early money = early gears = unstoppable.

FLASH

Good spell to escape. I think it is better than Ghost because as a Blitzcrank you are pretty fast especially when you will use a Overdrive so you do not need more speed. So you can just run using your skill and jump through the walls using Flash what is more effective.

MANA BARRIER

It creates a barrier of 50% of your current mana when you are under 20% of your life for 10 seconds. So if you got 2000 max mana points and you have lose 600 mana during battle and you got under 20% of your life you will gain shield which absorb 700 ((2000-600)/2) incoming physical or magic damage for 10 seconds.
Great passive which helps you survive many times, often when you think you are going to die or when enemy trying to finish you by ignite.

ROCKET GRAB

Blitzcrank fires his hand, which grab enemy, deal damage and pull him to Blitzcrank.
Your main skill with a long range (1000) but high cooldown so use it when you are really sure. It also has high mana cost, 140 mana is over half of your base mana at 1st level. Anyway deals nice damage and is great to pull enemy into your whole team. Also great to pull surprised enemies through the walls.

OVERDRIVE

It increases Blitzcrank movement speed and attack speed for 8 seconds.
Great skill to chase and avoid enemies. Also with 40% cooldown reduction from items you can maximum decrease this cooldown to 9 second what means you can constantly speed up yourself.

POWER FIST

This skill will hit your enemy for 2x of your attack damage and pop him up in the air.
Used with Rocket Grab let you gain some kills at the beginning of the game, especially when you pull target near friendly tower and stun him using Power Fist, there is no way to survive this. It also has low cooldown and cost only 25 mana so you can use this to last hit enemy minions.

STATIC FIELD

Passive: Lightning arcs off of Blitzcrank to hit a random nearby enemy every 2.5 seconds.
Active: Deal magic damage and silence nearby enemies for 0.5 seconds.
One of the best ultimate. On the 3rd level it hits for 500 + 100% of ability power. You can also decrease the cooldown from 40 to 18 seconds what means you can use it to kill minions.
Passive is good also to hit random enemy during fight you can sometimes get a kill because this skill deals 300 + 25% of your ability power.

1lv - Rocket Grab, it is your main skill
2lv - Power Fist, those two skills are "must have" for a simple combo
3lv - Overdrive, let you chase enemy or run away
4lv - 5lv - Rocket Grab, not counting Static Field it is only one skill increasing damage after lvl up skill
6lv - Static Field, now you are able to kick hard some ***
7lv - Overdrive, you can not take Rocket Grab so take this to increase movement and attack speed and decrease cooldown
8lv - 9lv - Rocket Grab, just lvl up this one as fast as you can
10lv - Overdrive
11lv - Static Field, now you should be able to kill whole minions group (without tank), of course lvl up always when you can
12lv - 13lv - Overdrive, complete this skill
14lv - 15lv - Power Fist, this only decrease cooldown of this skill so lvl up only after Rocket Grab and Overdrive
16lv - Static Field, of course...
17lv - 18lv - Power Fist, finish this skill

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First start with those items, you need extra 200 mana because of expensive spells from early game, especially Rocket Grab, which cost 140 at 1st level. Additionally 2 Health potions will let you survive longer, however its is not necessary.
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Try to buy Catalyst the Protector as fast as you can. It will give you a lot of health and mana after level up. Do not buy Boots of Speed before that item, Overdrive will let you run away or chase someone.
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Buy next Ionian Boots of Lucidity for more movement speed and what is more important a lower cooldown.
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Now concentrate to buy Negatron Cloak and Chain Vest that is very important but do not try to buy whole item build, it is not needed now.
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You should be not so easy to kill, so buy a Blasting Wand and head to the Rod of Ages.
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Buy next Glacial Shroud for more cooldown reduction and mana but do not buy Frozen Heart it is too expensive to lose your money.
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Buy again Blasting Wand and head to the Abyssal Scepter, which is great cause of reducing magic resistance of nearby enemies. So it is work great with combo Rocket Grab and Static Field.
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Now when you got the main items you can start to completing the Lich Bane, however if you do not have a lot of money start of buying Sheen what double your hit, additionally with Power Fist it will be 4x your attack damage hit. Anyway this is a great item for Blitzcrank there is everything what he is need: magic resistance, ability power, mana and movement speed of course.
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Now the game should be end but if it is not:


Complete your Frozen Heart build what gives you extra 50 defense and reduce attack speed of nearby enemies + 5% reduction of cooldown and buy Rabadons Deathcap for great boost of ability power.