This combo is quite difficult for a lot of people, this combo requires fast fingers and good at landing skill shots while moving. Although people say Rengar is a very easy champion, which he sort of is, he does require some skill for this combo. And no the combo isn't jumping on an enemy and smashing your face into keyboard.

The Oneshot Combo - (Have 5 Stacks of Ferocity) First I would use Sweeping Lens on current area or Raptor Buff(Razor Sharp) and press Ultimate, find the enemy, and when your approaching target use Youmuu's Ghostblade, follow up by using Empowered Q as your about to jump, and right in mid air or as your just about to end the jump use E then finally use W and Ravenous Hydra as you land

The (I'm to lazy to read) Combo - 5 Stacks of Ferocity > Sweeping Lens > Ultimate > Youmuu's > Empowered Q > Mid air E > W + Ravenous Hydra

Tips- When Ulting you should always go for the ADC or Mage (Duh). Also Rengar can also engage team fights, I do this all the time and win most of them, when their all grouped I jump at ADC or Mage depending who isn't their, and my team follows (Obviously you should tell team what your doing).

Works Well With- Orianna: It's fun having Orianna on your team if your rengar especially when she is support, what she can do is, when you ult Orianna can put the ball on you and when you gank her lane, she can press Ult as you jump on whom ever making it a deadly Wombo Combo. Bonus- If their is a Yasuo mid lane, dem plays