Welcome to my first guide, here i will teach you how to build an assassin Blitzcrank. Blitzcrank is today known as support, but, his AP scalings are very huge, making him able to 100-0 any squishy with a single grab, making him a very safe assassin, if you don't grab a tank.

For Runes we take MPen Marks, Armor Seals, Scaling AP Glyphs and AP quints.
This is for Late Game burst on carries, the runes provided will help you to kill any squishy you see.

I decided to take 21/0/9 Masteries because i found the utility route very good on , because after all, your early game is a little bit bad (unless you kill underturret) and you have mana problems early, and, also Fleet of Foot will help you on your catches.
Another thing i forgot to say is that if you grab the right person, you won't take any damage :)

This build is focused on Burst and Speed, Blitzcrank loves speed, and that's pretty good when your w is down, or if you want your w to be really effective.
If you are having a hard early game, i recommend you to switch Tear of the Goddess for Rod of Ages, it gives you very good sustain, and gives you mana, making your passive to be usefull anyway.
I get Rabadon's Deathcap late because you will only be able to instakill with your Void Staff , so, i prefer getting Rabadon's Deathcap very late in the game.

You'll max Rocket Grab first for damage, and Overdrive second, as you aren't peeling your adc and spamming Power Fist.

Mana Barrier : This is your life saver, this is why you build mana, believe or not, this will save you a lot of times.
Rocket Grab : Blitzcrank's specially known for this, and this little spell wins games, but also there is another way of surviving a grab without being a tank, and it's having a superior burst and speed, your passive also helps you escaping from a bad grab.
Overdrive : This skill, even with the slow debuff is very helpfull, it helps you with your grabs or escaping, a perfect skill for Blitzcrank's kit, use it wisely.
Power Fist : This is what makes your grabs so efficient, it makes the enemy Airbone, so, you can just press R and kill your target.
Static Field : This is what defines AP blitzcrank most, if you can't assassinate anyone, you can just get to the fight, use this, and do very high amountes of damage, think of it as an instant Death Lotus .

Well, your pre-6 farming sucks, you will need to last hit properly to get a very good CS, but, at lv 6 you can just press R and clear the wave, pretty easy, huh?
But you can farm while doing some real damage to your lane enemy.

Pros:
+ Very high burst and utility
+ Tanky with passive
+ Destroys low ELO
+ Safe assassinations
+ Fun to play :)

Cons:
- Skillshot reliant
- Grabbing the wrong target may mean your death
- Squishy without passive
- Easily countered by high mobility champions
- In low ELO people might rage you :(

Well, this is my first guide, i hope you enjoy it, tell me the results and feel free to comment or say if something's wrong, or even indicate me to add something. You can also help me by adding matchups.
Don't forget to upvote or downvote! Your feedback is reallu important! And i'm up for you criticism! i really appreciate it!
Actually learning codes :)