This build is probably the best out there for jungling Fiddlesticks if you want to have LOTS of fun. First off, you have to start the game with an /all chat: "I dedicate this game to my girl Wendy in honor of her delicious Stack Burgers." This lets all the players know what they're up against, I begin to cringe in fear. You will be getting stacks like none other each gank, so make sure you have a pun ready after each assist/kill for /all chat. I prefer "TIME TO GET STACKTIVATED," (you can use this one just before you ult in.) I also enjoy: "IT'S THE STACK ATTACK," and in the case of a multi-kill: "I'M GETTING KILLS STACK-TO-STACK." You should be doing it right if the other team rages back at you. So let's get stacking and see what we're working with. (This guide makes Jungle Fiddlesticks really fun if you are already comfortable with him and you know the right time to gank, but I'll also talk about that later.)
Magic Pen Marks for any MR they might get, Armor Seals for the jungle, AP per level glyphs to become awesome later in the game as you get STACKALACKIN'. The quintessences are really up to you, I had AP quints already and they work fine, but MS quints would be great to gank and keep up with enemies during your ganks to keep them in your Crowstorm damage range.
21/9/0 Masteries. It's a decent strategy, but you could go some other ways, like 0/9/21 or 21/0/9 or 9/0/21 depending on whether you want longer buffs and faster regeneration/CDR, more damage and longer buffs or some damage and longer buffs/regen/CDR (respectively.) My masteries here are for armor in jungle and damage in ganks, but even I'm reconsidering that. Either way you go, you're bound to get STACKIN' with proper timing.
Mejai's Soulstealer, the item that makes this so much fun. You're gonna love this item after you pick up a few kills or assists, then go crazy when you hit 20 stacks with your extra CDR. After Rushing Mejai's get boots for movement, then Sorcerer's Shoes for the Magic Pen and the extra movement, both critical in ganks. The rest of the items are your preference, I love Will of the Ancients because of the Spellvamp, and sometimes I pick up the Hextech Revolver by itself for more SpellVamp, and even then if someone else on your team has the WOTA Aura during a gank or team fight, you have 52% spellvamp. You pick up health off of Drain and then more health on 52% of the damage you do, then if you popped Crowstorm to come in, you have RIDICULOUS health Regeneration (imagine if you got the regeneration utility masteries :D .) So with that you can also get Rabadons for more AP, more damage and healing. Rylai's for more HP, more AP, more damage, more healing AND a partial slow. Zhonya's to ult in use silence and fear then become invulnerable while your team cleans up. Looking good with those Stacks, Scarecrow.
Basic stuff, Drain for jungle at level 1, Darkwind for damage and silence, then Drain and Terror (you can gank once you have Terror, but be careful, I still recommend your Ult to gank if you're not experienced enough to tell if you can secure the kills.) Drain first, then Terror to keep them feared and in your damage range, Ultimate whenever you can level it and Dark Wind last.
Smite for jungle, Flash for placement in ganks with your ultimate (double blink,) but if you're lower level, take Ghost so you can keep up with whoever you're ganking. Not much else to say here.
The most important chapter: JUNGLE TIME. Get a leash on your Blue Golem and take him, you should be level 2 after that, so get Dark Wind and use it on wolves to damage and then drain Big Wolf. Don't be afraid to use abilities, you'll regain your mana quickly with blue (even more with Utility Masteries.) Proceed to Wraiths, Dark Wind initiate, Drain Red Wraith, finish the rest and continue to small golems. Finish those with a Dark Wind on golems and Drain the big one. Proceed to Red Buff, Dark Wind, Drain, Drain, Smite and finish them (Later on 1-2 Drains and a Dark Wind clears the camp.) So at level 4 you *can* gank, but be careful, look for a lane that's pushed to your turret, go around the river/bush, Dark Wind for the silence, Terror to keep the squishy nearby and then Drain the squishy champ to take them out. Teamwork required on this one, so ping and make sure your team is ready for it. You can take out the Dragon with some teamwork early, then Solo him later on, so look out for those opportunities. For the rest of your level 6 and above ganks, Ult in and have fun silencing, fearing and Draining with your teammates. After all your ganks, prepare the other team for the: /all "STACK ATTACK."
It's really simple. Make sure your team is ready to go. You can Ult in, Dark Wind and Terror someone to initiate only if you have Zhonya's to protect you from damage. If no Zhonya's and you're a Badass living in STACKCITY then you can still do the same as long as your team follows to clean up. If you're not a Stacked Badass, then make sure your tank initiates or something, then Ult in while they're fighting from a bush. Always Ult in from a bush so that your channeling can't be interrupted by CC. Keep the stack puns up, remember that this game depends on your puns.
FOLLOW THE GUIDE AND GET STACKIN'!
(I also recommend that you have lots of creative stack puns in your arsenal, ready to whip them out at any time, this game is only successful if you annoy the other team.)