Fiddlesticks excels at ambushing from unseen locations with his Q (fear) and W (drain) combo, delivering heavy burst damage and potentially turning teamfights with his ultimate.
He is highly vulnerable to hard crowd control (CC) from champions like Galio, Zac, or Leona. Twisted Fate's ultimate can also deny his engage.
Build grievous wounds to counter his strong sustain. Fiddlesticks requires high skill, as a poorly played one can be a liability to the team.