i don't think this is the best jungle fiddle build but i use it a lot with good results.

Pros
has a 3 second fear at level 5
fear makes easy ganking.
once drain started it carries on until they are well out of it's range
can ult over wall.
cons
squishy early game.
doesn't go well with heavy cc.
Long cooldowns.

Now obviously as fiddle you start at blue, now tell your mid laner you won't be giving them blue because you NEED it if you don't get it then you will be either recalling a lot or spending a lot f money on mana regen items or pots etc.

When you reach level 9/10 grab a blue buff if you haven't got one and go solo drag, if you want help ssk but you can solo drag at this level

fairly simple run in fear dominate your fear should last long enough even at level 1 to stop them long enough for your teammates to jump on them, so you get a free kill.

i use these particular masteries because i think it is what is most beneficial for jungle fiddle,you don't need any defense pints because of your drain, you will nearly always be full health, because of the items the extra move speed is useful as you won't have full boots until maybe 13 mins in game, the rest i think are fairly simple reasons; the mana for more sustain in jungle and while ganking, the cooldown on summoner spells for more frequent smite use clear quicker easier to counter jungle, the exp for faster levels and the spell cooldown for more drains :D