RENGAR BALANCING WITHOUT CHANGING NUMBERS
UNSEEN PREDATOR: While in brush or in stealth, Rengar gains bonus attack range and his basic attacks cause him to dash to his target. This bonus lasts for 0.5 seconds upon exiting brush or stealth. Unseen Predator occurs regardless of whether or not his target has Sight_ of him._
Why don't simply take aways his ability to use Unseen Predator if he's spotted by wards or pink wards? It make sense and will be a simple and great way to add a counter to him. Denying his gap closer if you have good vision cover is a great way to balance him.
Think about it, if Rengar is coming to gank you adc now, there isn't much you can do unless you Madlife him while he's steath. With this change you can simply put a pink near you, and he'll have to walk all the way toward your adc and with that window you can punish him, or he'll be forced to back off and waste a gank+ult.
C'mon Riot, is this asking too much? Really?
