Hello,
this is my first guide and my native language is german, you will find many grammatical errors in this guide, feel free to contact me or post them in the comments^^

also it will not be that comprehensive like other guides are but I think this is a very fun build for Fiddlesticks and I will complete the guide in the next time.

I hope you will enjoy it (at least a little bit)

If you think that you got enough magic def late game you can also use Greater Glyph of Force, it stacks nicely with Rabbadons ;)

the other runes are the only viable choice I accept! :p because I really hate flat AP runes and ALWAYS prefer Magic pen over them, besides they got a nerf.

There are many viable choices, but Flash or Ghost is a must have for Fiddlesticks, because he needs them for his ultimate!

other viable spells are Ignite and Teleport

It's hard to last hit with Fiddlesticks and if you got the AD Carry on you lane just don't do it.
If you got low life just drain a cannon mob and you will be ready for the next fight!

This Guide heavily focuses on Drain, that's why we will level it first and after that Terrify, always try to get near your enemies to Terrify them and than Drain their Brain, don't let them fear you with the damage you may take, you will likely get it back ;)