User blog comment:Emptylord/Champion reworks/Butthurt Patch Notes/@comment-15077371-20160519193445/@comment-3974211-20160520034627

It's "only" 100% armor penetration on an attack if it would kill the target, plus 50 bonus damage. This is a relatively low threshold, especially for a champion that usually rushes early armor penetration and does true damage versus base armor any way. This is likely a nerf compared to the 10% of maximum health damage his innate currently gives him.

Making his attacks more sluggish is an option.