Okay, so this is my first build. Any/all suggestions welcome to make the guide better, please do not down vote without allowing me to make changes/updates based on your constructive criticism. This build shows how I enjoy to play Fiddles, and I do quite well. It is a little different then most Fiddles builds, which is why I am posting it, I'm sure there are those that will disagree with certain item selections (I myself only put the 2nd deathcap in there because you never really get that far anyways, but if you do, I can't think of a better item to hold the 6th spot then a needlessly large rod -> deathcap.)

This will not be a definitive guide of where to hide to use your ultimate, there are a ton of places that are viable, some more used then others, and some dangerous to wait in too long. Best advice I can give is to experiment, and bring flash with you as it opens up a lot of places that normally would be just too far out of reach to use properly. Also, ulting from a close bush and then flashing can really help to keep most of their team inside it's range while you pick one to kill with Terrify + Drain, but more on that later.

Quints - Flat health helps immensely at level 1, and is a staple in most builds. With Fiddles low starting health this is highly recommended to allow your Drain some time to work.

Marks - Magic Pen. Since I don't go Magic Pen on the boots, this is a must to help out early game.

Seals - Magic Regen per level. I prefer these to give me a boost in laning power early game. Also helps out mid to end game allowing you to spam drain as often as you need it. Another viable option I stopped using was flat health, and health per level. I found the extra time or two on drain was much more useful then a few more hp (Especially since I put Rylai's fairly early in my build to keep Fiddles health up.)

Glyphs - 8 flat Cooldown Reduction, with 1 Cooldown Reduction per level. The 1 rune per level allows you to cap at 40% cooldown reduction. Without it, you end up with 39.84%. Not a big difference, but I like to have the flat number by level 12 :P It is worth mentioning that I don't think going all per level is as beneficial. I tried not getting a fiendish codex but going all per level, and it seemed to really hurt my pre level 12 game, and didn't quite catch up to the cap of 40% by end game anyways.

I use the utility tree for a few benefits.

Mana regen and health regen is buffed by a decent amount, allowing your drain to be more useful and keeps you in your lane longer.

Experience is an absolute must, since Fiddles does not have to return to base to heal almost at all, (and I prefer to middle lane or top lane with him) he can out level his opponent extremely quickly. I have often shut out my opponent from xp as early as level 1 forcing him to return to base, and by the time he returns I am level 3 with a fear + 2 points in drain now. If he couldn't kill you level 1, he will have a much harder time at level 3 :P

Movement speed. Helps out a bit with escaping, but it's real benefit is getting that little bit further when popping your ult + flash.

This is where I anticipate the most controversy since my item build is far from standard. I find getting to 40% CDR by level 12 (mid game) is more beneficial then rushing another item such as Archangel's or the deathcap. Also, I usually will have at least the giant's belt by this time, so having 2000 health is helpful by mid game. Generally speaking, with the increased uptime for my ult allows me to use it in many different ways then just a team fight initiator. Since you should be hitting level 12 before your opponent hits level 8, I usually have the mid tower down by level 12 and begin ganking the side lanes. Since you can get a double kill on bottom, and by the time you walk to top you have your ult back, it can really turn the tide to your advantage just before team fight time starts late mid game -> end game.

After the deathcap I grab archangel's for the huge boost to mana, allowing you to now stay outside of base forever. After that if the game has lasted this long I'll turn fiendish codex into a deathfire grasp (this doesn't happen very often which is why I rune the way I do for 40%at level 12) and if you're dying for another item somehow another deathcap is always a good boost of AP. This is where I myself have the most debate if it gets that far, so please feel free to offer suggestions for a really late game.

Drain Drain Drain. Since I don't grab Dark Wind until I have to, it limits the farming potential of my early to mid game. I have never found this to be a huge nuissance as far as gold collection. In fact, I prefer it this way because Fiddles autoattack is so weak he can keep hitting minions and stay at the same spot in the lane (where other champions have to pay attention and only last hit to accomplish this.) Also, the way I play Fiddles doesn't leave much time for silencing an enemy for 1.2 seconds anyways, and I've found the travel time before the first hit of silence allows most other champions to utilize their escape mechanic or rush into you anyways, making it quite useless as a first spell. Remember also, with the cooldown reduction you'll have, you can fear, drain, fear drain, in about the same time you'd only be able to get one of those rotations off. This can really mess up your opponent as he is usually banking on one thing: Missed rotation, usually due to them surprising you or silencing/stunning etc. A missed rotation without CDR can lock Fiddles up pretty severely early game.

Teleport - Bread and butter of 5v5. If you don't take teleport, I'm not sure why :P

Flash - My preferred 2nd, to allow you to gain a lot of extra range after your ult, and always a great escape mechanism. I can't count the number of times I've flashed through a wall, or behind a bush preventing 2-3 champions from chasing simply because they have to walk around. Especially end game, I flash out of their base and escape all the time.

Other Options: If you are playing a 3s, teleport becomes less useful and I would swap for either Ghost to get you a little further on your ult. Or Cleanse to prevent stuns/silences from messing up your rotation too much.

This is my first guide, and I will be making updates as patches are released and I receive feedback from the community. Again, constructive criticism is welcome and I look forward to debating the finer points of Fiddles play with you all. If you liked my guide and won a game with it, let me know :P