Hello, my name is DJMurphster, and I main Fiddlesticks in the jungle. Although I am no pro, I do believe I know my way very well around this champion, and I hope you get something out of it. Enjoy my guide! And enjoy this Instalok song from 2014...
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Pros
- Easy to farm with
- No skill-shots
- Strong CC
- Hard to mess up with
- Great at teamfighting
- Great passive that synergies with Crowstorm
- Has great engage, and amazing re-engage
- Has the most fun skin in the game

Cons
- Squishy
- Super vulnerable to invades
- Low early game damage
- Countered with vision control
- Useless without Crowstorm
- Not forgiving
- Not very good wave clear
- Fairly immobile when running away
- Depends on good positioning for success

"Why Movespeed Fiddle?"
Well this build revolves all around Fiddle's passive, A Harmless Scarecrow. All these movement speed buffs and Rylai's Crystal Scepter, plus his passive makes you extremely quick and sticky. It is extremely hard for the carries to escape from the clutches of his Crowstorm

"Why would you go Stormraider's Surge instead of Thunderlord's Decree ?"
Well I can tell you that although Thunderlord's is viable and helps with your overall damage, it doesn't help as much as Stormraider's with his updated passive. I would rather have the ability to chase fleeing enemies with his ultimate on, rather than a little tick of damage that wont actually matter later on in the game.

"Why go Tracker's Knife instead of Stalker's Blade?"
Tracker's Knife gives you the ability to ward without having the Stealth Ward, which is great considering you want to have a Sweeping Lens and Oracle Lens to stay out of sight. Also, Chilling Smite has 500 range, while Terrify has 525 range, making Stalker's Blade unworthy. Although you do steal movement speed, therefor making you faster, having vision is substantially more important than stealing 20% movement speed. Stalker's blade is good for junglers that have no movement speed steroids, like Rek'Sai.

"When would I max Reap over Terrify second?"
When your team either already has a substantial amount of cc, or you are the only ap-carry. Although alone, this ability is pretty weak; the silence can hit multiple targets, but is only active for 1.25 seconds. Plus the silence is not instant-cast, you have to wait for the crow to connect with the champion for the silence to take effect, making it unreliable. What is really great about it is when 2 carries stand right next to each other and the crow bounces all 7 times between them to get a nice chunk of damage, but it's very circumstantial, which is why I normally just use it on the carry after I use my ult and q to maximize damage output.

"What boots should I choose?"
I would recommend Boots of Swiftness most of the time, but some other viable options would be Ionian Boots of Lucidity and Sorcerer's Shoes. With the new passive on Boots of Lucidity, it makes it a very good option for Fiddlesticks, as Crowstorm + Flash = good things, with good setup of course, and the more frequently good things can happen, the faster you can close out the game. Sorcerer's Shoes help with damage, but that's about it. Get them when you're either the sole ap-carry of the team, or the carries you need to kill are very low mobility and easy to lock down.

"Why go Boots of Swiftness over Mobility Boots?"
Quite simply, Boots of Swiftness work while in combat, while Boots of Mobility does not. Now I understand getting in the right position is key to playing fiddlesticks, which is why you could argue that Mobi boots are the better choice. However, in combat Mobi boots only provide a measly 25 movement speed, making you easily out-runnable against all other option of boots. After that you could also argue that while being in stasis by your Bountiful Harvest or Zhonya's that movement speed is completely useless. While you are right, after you cancel your Drain to chase (which you should always do, Crowstorm does more damage overall than Drain, and requires you to be in close enough proximity to allow your abilities to cool down to use them once again and you aren't stationary dealing damage) or the Zhonya's stasis runs out? Most likely after one of these 2 things happen to you, your enemy is running away from you. It's impossible to give chase with Mobility Boots, which is why Boots of Swiftness are superior.

"What should I be asking myself when i'm looking to gank someone?"
Well, high mobility champions aren't the best to gank early, because you haven't put points in his Terrify yet, making it easy for them to escape the damage of his Crowstorm. Be aware of the possible locations you can blink from with your Crowstorm, and also be wary of vision control. With the 1.5 second channel of Crowstorm, you must make sure the enemy does not know your location, as they can react during that 1.5 seconds. His early ganks also lack damage pre-6, as well as gap-closers (minus flash). Don't over-estimate the sustain of his drain, as it heals for the amount of damage done, and your damage is actually pretty low early. Don't under-estimate the power of your ultimate, it is a very strong tool and often leads to successful ganks with the proper set-up. You also might have started noticing the pattern; the success to Fiddlesticks relies solely on positioning. Just keep that in mind when you are about to ult into the wall... Play Video
'Nuff said
Be sure to ask questions in the comments so I can add to the FAQ!