Blackfire is strong AP Assassin with very interesting kit and mechanics. Her main lane is mid, but also she can be played on top or jungle '
Blackfire is not so hard to play. She can easy win mid against champions with hard mechanics just fearing them with Q and knocking them up with the ult. They will have disabed abilities and will cannot cast his complicated illusions. And finally she will do the killing blow with the passive.
Remember that she has movement speed buff and shield and gains CC reduction if destroyed. If somebody is gonna wreck her on the lane - she can try to escape.
Blackfire's innate triggers only if the target is below 30% health. Dont miss it! If the target is in your range dash instantly, before the tagert receive incoming healing from, , or just life steal or spell vamp.
The Q is the spell that can help you with champions such as Zed, or Kassadin that can can easy escape from you. Using Ult to disabe their movemet speed and abilities and after Q make an unescapable combo. The enemy will not be able to cast any abilities for up to 2,75 seconds. Then they won't outplay you.