Recently Rengar has been adjusted with what Riot are calling, well, an adjustment. With the scope of the changes though, it was a mini-rework. Now it's time to balance the rework out.
The goals of Rengar's update were to smooth out Rengar's gameplay, keep his current playstyle, and clarify his builds.
It consisted of keeping a close eye on the Q crit damage ratio so he doesn't get too out of line, while also knowing that Q no longer applying on plants can be painful for seasoned players who used this mechanic to optimize Ferocity stacks.
However, the changes to his Q had an unintended consequence of making Rengar quite the tower-taking champion. To combat this, Riot are nerfing the damage his Q can do to structures by 40%.
However, to balance out the nerf, and steer the champion towards the jungle once again, Rengar's W ability, Battle Roar, now scales better against monsters, with its scaling being 85 to 150 magic damage, from ability levels one through five.
As the developers state, the fact that Rengar's Q has become a tower-taking juggernaut is not something they wish to remove completely, but it is something they don't want to see taking over his entire personality.
In addition, the buffs to his W ability are mainly instated to offset the nerf Regar received the last patch, in which plants no longer give him Ferocityu stacks.
And, finally, Riot have also fixed the bug where Gromp would not give Rengar a Ferocity stack, thus ruining his jungle clear.