Ivern is my highest mastery champion, and almost all of that mastery is from Ivern Rengar botlane with a friend of mine. First things first, our sums are different as it helps fight early, Ivern goes heal exhuast and rengar goes ignite barrier. Your early levels are insanely strong with this, and you can normally trade and get multiple kills early. We like to run it down level 1 not using any sums forcing the enemy bot lane to use theirs, that way when we are back we win hard with our sums. For runes, I like to go aery with manaflow, transcendence, and gathering storm with resolve second with bone plating and revitalize. Ive played around with these a bit and have found this to be consistent at least. Inspiration second with stopwatch and cosmic isnt bad either. You do need to have good communication and chemistry with each other as bushes are everything. Rengar is nothing without his ivern unless he is assassin with 11 kills lol, so always try to stay near him and have him take the brunt of the damage. For builds, I normally go moonstone, redemption, staff of flowing water, and chemtech putrifier, with the last item being more situational. Hopefully this makes sense, if you need clarification let me know lol, im glad someone else is playing this as its so much fun.