Threats to Fiddlesticks with this build
For some reason I think "Surprise Party Fiddlesticks" and "Dark Candy Fiddlesticks" skins make Fiddlesticks act strange. I don´t know Risen Fiddlesticks and Union Jack skin, so for me Bandito, Pumpkinhead and Fiddle Me Timbers or no skin are the best skins.
Use your E to deal damage, but take care ganks cuz it can push the lane pretty easy. When enemy is with low life you can try to go all in (take care of your mana) or wait for your ult to finalize your enemy (RQEW), especially when you have flash on.
If enemy ganks to push your tower
If too much enemys gank mid to push your tower, you can hid in jungle and ult+flash+E+Q+W and if you need use Zhonya too, with your ult all minions will die pretty fast and the tower will focus on one champion and it's easy kill for you, just take care with wards.