AP Rengar`s strength is being able to 3 shot. To accomplish this get 4 ferocity than use your ultimate then Q while your stealth. Afterwards, right click an opponent and then use your empowered W and then a normal W. If this is not enough to kill your target. Don't worry and wait for your ultimate`s ferocity charge and empowered W again. In addition, you will be able to escape anyone with ease with Luden`s Echo % speed increase and your bola strike.

Pros : AP Rengar has more burst then AD Rengar. This is good for destroying hyper carries such as Vayne. However, AP Rengar doesn't have much consistent damage. This is a disadvantage but who will need consistent damage if you can 3 shot someone.

Cons : AD Rengar has a lot more use in teamfight being able to kill multiple enemies without stopping. This is good against tanky team that you cannot 3 shot with AP Rengar but in my opinion, their both very good at bursting enemies.