Ivern is not a champion.
Yup, Ivern is not a champion. He is a Rengar's helper. Just like Braum is Lucian's helper.
Works well with: Rengar - the Pridestalker This one is obvious. Kitties love brush, and Ivern can make plump patches of turf appear literally anywhere. Duo up as the Pridestalker and the Green Father to let the hunt begin.
That's really disappointing. Don't get me wrong. You can play Braum without Lucian and You can play Ivern without Rengar. But eventually you will see the difference. Making such obvious champion synergies is a dead end. Either Ivern will be decent without Rengar and over avarge with Rengar, or Ivern will be balanced with Rengar but weak without him. Then again That doesn't mean Ivern will lose every game without Rengar or Ivern will win every game with Rengar.
I know Riot is really experienced company, and I exactly know why they are making such synergies. From LCS point of view it's more interesting. Ivern is definitely is going to have a new unique impact on champion select, but... I already feel bad for all future Ivern mains, who mastered Ivern and can't have a great game without Rengar. I bet Rengar players feel great tho. Finally they can jump from the middle of a lane. If I were Riot I would give Ivern an ability that also doesn't benefit Rengar at all, like ability to give mana on his shield. That would be pretty fair. Rengar having synergy and anti-syngergy with Ivern at the same time. This example i still not perfect. I am really confused. I want to love Ivern, but it's hard to, as I already see that for many players it will be really frustrating to play with or against Ivern.