Welcome on my first Blitzcrank guide on this side. This is guide for supports, but you can make this build on middle, too. I am the Blitzcrank main and I have 200k points on blitzcrank and I played a lot of games on this champ. Below I will explain a bit more about this guide. If you have any questions feel free to ask. I will try to answer for comments.

+ Enaging fights
+ Easy to take down carries
+ With this build you can take down assasins and ADC solo
+ With your Rocket Grab you can easily make some kills in early
+ Your Static Field is silenting, so you can easy counter for example Samira's R

As support you can help your ADC make some kills in early really easy. Only one Q can cause that enemy die in few seconds. In late game your role is taking ADC or other weak champs to take them out.

- One wrong Q causes that you lose fight
- No heals/shields for your teammates.
- Early is in your hands, but in late game you have to trust your teammates.

Really important is to make sure you gonna grab ADC or other weak champ, because if you grab tank it can cause that you will lost fight, because they can engage into you. In early take care about your ADC position. Don't grab when your ADC is in really close range to you, because it can cause that your ADC die.

There is nothing special in the summoner spells. Of course you should pick the most obvious summoners like Ignite and Flash but sometimes Exhaust will be better than ignite. For example against Samira which need to be in closer distance.

Beggining
At the start item you should go Relic Shield with 2 Health Potion and Stealth Ward. At the first recall you gonna buy items needed to create Hextech Rocketbelt, some Health Potion (about 2), Control Ward and Boots. So you should have about 900 gold at first recall. At the second recall you gonna buy Mobility Boots (remember that you are still support and your adc needs you). When you get Mobility Boots let's buy more items to build Hextech Rocketbelt.

Why those items?
Hextech Rocketbelt - rocket belt is really important, it give you dash and movement speed after using it. This passive with your W makes you really fast so you can chase enemy easier.
Mobility Boots - I think most supports should buy mobility boots, that make you can come back faster at the lane.
Zhonya's Hourglass - Zhonya is really important too, because can save you in a lot of situations and this is core item for a lot of AP champs.
Horizon Focus - Your damage is increased by 10% for 6 seconds, when you hit someone with your Q. It works really good at blitzcrank because after you hit someone with your Q it make that your E and R deal such a more damage to enemies. Especially in late game when you reach more AP.
Lich Bane - It makes your E deal more damage after you hit someone with your Q.
Rabadon's Deathcap - This is next one core item on a lot of AP champs. It makes you deal more damage because Rabadon's passive give you 35% more AP.

Dark Harvest - We are going to oneshot everyone so dark harvest makes it easier and in early causes that you deal a bit more damage when someone is on low HP.

Cheap Shot - there is second rune that makes you deal more damage to enemies.

Eyeball Collection - every takedown you gain pernament AD or AP so this rune give you more damage in late game, too.

Ingenious Hunter - It give you item CDR (including trinkets), so you can use your rocketbelt and trinkets more often.

Presence of Mind - blitzcrank waste his mana really fast so presence of mind will be really usefull because it give you some mana after takedown.

Coup de Grace - You will deal more damage to low HP targets, so you can one shot easier.

CDR
AP
HP (eventually armor or MR if enemy are full AP or AD)

Blitzcrank is losing the most often against tanks because if you grab tank even by mistake it can make you can lose fight because for example Leona can stun you or nautilus can root you. But of course Morgana is the biggest counter because of her shield and long CC's.

The best synergis are adc which have CC for example Jhin W or Caitlyn traps. Miss Fortune can work really well too, because of her slow. The worst syniergis are champs with no CC and champs which can't make a lot of damage in few seconds.