This is something that I've thought would be pretty cool for Garen's R since they first gave him the VU back in 2013. Scoring a killing blow with Garen's R gives its VFX a huge AoE explosion that is centered on the victim and blurs the space around it in a radial effect. I thought that an interesting way to make Garen more of a competitive champion would be to grant his R an additional AoE affect, based on his VFX, if he scores a killing blow with R; perhaps something along the lines of an AoE knockback like a janna ult or an AoE slow. It beats just tweaking the cooldown instead for sure. Not to mention that it would be so freaking cool too.