Typical AP jungle mastery tree.

MPen Marks are very good for late game and work with Fiddle's passive very well. Combine that with the boots and abyssal scepter, you will do tons more damage.

Armor seals are great for the jungle and if they are AD heavy.

AP Glyphs and Quints are very good early game because you start off with almost 25 AP from runes, and 20 from the Amplifying Tome.

Smite - pretty obvious why you need smite.

Flash - flash is great because if you don't ult in the correct location, you can easily flash to where you wanted to go.

1) Will of the Ancients - Why not just a revolver?
Because it allows you for easy baron soloing and you will never die in teamfights. You can also easily heal after a teamfight instead of recalling and easily can push a lane.

2) Sorcerer's Boots - Why not Merc. Treads or different boots? Fiddle's passive is good enough!
The extra MPen works great with your runes, masteries and passive. It allows you to do more damage, killing squishy carries with only your ultimate, and saving the Drain you would have used on them for someone else.

3) Zhonya's Hourglass - Great item that allows Fiddle to never die in teamfights and allows easy initiation and survivability. It also gives some armor.

4) Rabadon's Deathcap - Great item that gives tons of AP.

5) Abyssal Scepter - Reduces Magic Resist and also gives Magic Resist and AP. Good item that can substitute for a Banshee's Veil.

6) Rylai's Crystal Scepter - Really any item can be replaced for this. This item gives good AP and HP, so it is my favorite choice. Other items can be used instead of this though.

(SUMMARY AT BOTTOM)

Ask for a leash on blue. Depending on how many people protect you and/or leash it, you may only need to drain it 2-3 times. Smite the golem and move on to the wolf camp.

Drain the big wolf and focus on auto-attacking one small wolf. Drain the other wolf and auto-attack the last wolf to death.

Move onto the wraiths and use Dark Wind on a red wraith. Drain the blue wraith and auto-attack the red wraith with the least health. Drain the wraith with the most health, and auto-attack the last one.

Next is double golems. Start with dark wind and immediately Drain whatever golem you didn't throw the Dark wind at. Throw more Dark Winds and Drain until they are both dead.

Grab red buff and smite it to kill it.

Now there are a few options:
1) Gank bottom or middle lane. Your fear will be good enough that you can easily pick up one kill.
2) If the enemy team has no jungler, you can move over to their blue buff and wolf camp. If they do, it is best to recall.

You should have used your health pot whenever you felt you needed it (usually during double golems or before red buff).

Complete your Hextech Revolver, get boots, and go back to the jungle. Wolves and wraiths will have spawned again and you can kill them for the gold and EXP. Now you should be level 6. Level Crowstorm and get the blue buff. Without it, your ultimate will have a much longer cooldown. Gank whatever lane needs help.


(SUMMARY)

Blue buff > Wolves > Wraiths > Golems > Red buff > Gank
or
Blue buff > Wolves > Wraiths > Golems > Red buff > Recall
or
Blue buff > Wolves > Wraiths > Golems > Red buff > Take their buffs

Obviously you need Drain to jungle at first. Get Dark Wind at level 2 so that you can easily kill wraiths/wolves. Another point in drain at level 3 because you don't need to gank yet, and leveling drain will help you clear the jungle much faster. Getting two points in Terrify next is best because the longer fear can help you gank much more efficiently after you get Crowstorm at level 6. Getting a 3rd point in drain at level 7 allows you to secure dragon and gank bot when you are done. Max Terrify, max Drain, and with the WotA and Zhonya's, you will never die. :)