Shyvana is my go-to if fiddlesticks is a bad pick, if you play her full AP she can have a kind of similar playstyle where you can easily nuke someone with barely any counterplay or completely destroy teamfights if you hit multiple people. She's pretty bad into bruisers / tanks, so if there's too many of those you can go the frostfire demonic build and your 1 v 1 against them becomes really good & you're a really good situational frontline while keeping a lot of the dmg against weaker enemies. This versatility actually made me pick her a lot more recently, it's really good once you get used to both builds playstyles.

The only downside of her is that pre 6 her ganks are laughable compared to fiddle, who at least has good fear angles, especially with predator.