Fiddlesticks is a great jungle pick! Even though he is really weak Pre-6. Fiddlesticks offers a great advantage in teamfights and ganks to help your team get ahead. He heavily relies on his Ult Crowstorm in teamfights but if not seen by the enemy he fears like his Q Terrify. Reap offers a silence too so Fiddlesticks is great into teamfights! Fiddlesticks also has fast jungle clear with Bountiful Harvest leaving him with alot of HP left for GANKS!

Electrocute		The usual damage keystone. It enhances your single target burst and is the most reliable keystone when you expect to get ahead early. It can have some power in killing your enemies with greater burst and works well with your kit. If you are playing with this rune I have found this more consistant for damage than Dark Harvest. Another downside of this keystone is that it can be hard to proc on your target in large fights. Electrocute will only proc on the first target hit by three different spells. Works well with Gathering Storm so scaling is not an issue if you choose that path.
Dark Harvest		This is a great Rune for scaling. Damaging a Champion below 50% health deals adaptive damage and harvests their soul, permanently increasing Dark Harvest's damage. Dark Harvest Before it does not trigger off other procs (e.g. Scorch, Liandry's Torment) but can trigger with Luden's Tempest More testing will be done to confirm its the same..This rune is not consistant as Electrocute games can last 40mins or 20 mins meaning you do not get the max reward from Dark Harvest.

Liandry's Anguish		This mythic item UNIQUE Passive: Ability damage causes enemies to burn for 60 (+10% of ability power) (+4% target's maximum health) magic damage over 4 seconds and grants the user 5% magic penetration per second for 4 seconds against burning targets, stacks up to 5 times for a maximum of 25%. Mythic Passive: Empowers your other Legendary items with 5 ability haste. I found that this Item is the best for tanks as Fiddlesticks as it allows you to melt Champions and reduce healing with a 5% Magic Penetration that stacks to 25%. This item works well with all legendary items for Fiddlesticks. This item works well against Healing Jungles like Rengar and Nunu & Willump. Darius' Decimate, Renekton's Cull the Meek or Sylas' Kingslayer. It can also weaken burst healing champions such as Aatrox, Dr. Mundo, Fiora, Swain, Trundle, Vladimir, Warwick, or Zac. It can also Weaken Yuumi and Nami heals too.
Night Harvester		This item offers Fiddlesticks UNIQUE Passive: Damaging an enemy champion deals 125−200 (+15% of ability power) magic damage (depending on level) and grants you 25% bonus movement speed for 1.5 seconds (40 second cooldown per champion). Damaging new champions extends the bonus movement speed duration. Mythic Passive: Empowers your other Legendary items with 5 ability haste. Night Harvester offers Burst damage and Movement speed for Fiddlesticks. This item is great for your ult to get into difficult spots but does not offer the same damage as Liandry's Torment to Magic Resistance and Heals. I recommend pair this item with Morellonomicon and Void Staff for the Balancing effects of melting Tanks. However, I recommend Building this into a Squishy Comp as the burst damage will outshine Liandry's Torment
RiftMaker		This mythic item UNIQUE Passive: For each second in combat with champions, deal 3% increased damage, stacking up to 5 times. While this effect is fully stacked, convert 100% of the increased damage into true damage. Mythic Passive: Empowers your other Legendary items with 5% magic penetration. More TESTING needed.

I will Update on Playstyle and Ult spots in the Future. Hope you enjoy!

FEeeear.... :)