Ziggs is a VERY good mid, he's not really a counter to anyone in particular, nor countered by anyone in particular. Ill explain why Ziggs is your man for mid.

I chose the Magic Pen runes because, when you start smashing them, which you will, they will get magic resist, and you need it to try and cancel them out

The Ability Power on The Quints and seals is pretty self explanatory.
The mana regen is important because ziggs DRAINS mana with his spells, its very helpful so you don't always need blue

ABILITY...POWER!!!! juice that **** up
Utility wise, the mana regen and the speed help you zig and zag out of places.

These are core items that make ziggs a monster, I also sometime start off with a tear of goddess if you know its gonna be a long game, then you can do ALOT more damage later on, but this is a build if you want to make them quit early.

Bombs and Mines are where all of ziggs damage comes, you want to get them back to back, the c4 at level4 is entirely for keeping people off you or keeping them from running, you dont really need anymore points into it until late game

Flash Ignite Combo, First blood no assist.

Pros

He's very good at moving around
good burst and poke
Nearly global ult, can help your team if they are in need of it

Cons

There are no Cons to Ziggs, he's ****ing Ziggs

In summarization, Ziggs is a great mid, he can burst he can poke, he can save team from far away, he is the most easily playable mid there is, nothing really stops him. Get Ziggs,and Zag them *****es