User blog comment:Care Level/Itemization Holes/@comment-5761259-20130825054736/@comment-9593635-20130825142047

• "Armor pen is such a great early stat, yet flat pen falls off late game. It would make people like Riven capable of wrecking you with just tier two boots, which is not a good thing. There is a reason there aren't armor pen boots, it's just too strong."

I was thinking %Armor Pen rather than flat armor pen; like you said, flat armor pen is too good early and not good enough late. Percentage armor pen, like percent attack speed, provides a percentile boost to damage that scales as AD scales, so it stays relevant throughout the game without being too good at any one point.

• "As for the rapier, there is an itemization hole around high AD items, and I do really like the increased damage vs decreased AS, but the item would be too strong. Zed say could have like 50% bonus AD while this is active at lvl 18. 25% is already a lot, and even on someone like Riven who has around 400 AD, assuming the item gives 25% bonus, that's another 100 AD off a passive. If it were a flat bonus, say a 20 AD to a 40% AS reduction, that would be more acceptable."

The numbers can be tweaked; 20% bonus AD for 20% attack speed probably isn't unreasonable. I'm not going to do the math, but it should fit the following criteria: (1) Never ever worth it for autoattacking. If AA DPS goes higher with the toggle, either the AD boost is too high or the AS penalty is too low. (2) Provides more AD than a second Bloodthirster, but not as much AD on its own as a single BT. (3) Improves effective AD more than Last Whisper (we're talking about a very expensive item, as opposed to the cheap LW).

Also, because it's not giving lifesteal, you don't have to pay for lifesteal (it can give other stats, instead, to push the price up: Armor Pen or CDR are things that AD Casters welcome); I've always hated having to pay for stats that I don't need (I would build Sheen into Iceborn on Riven in a heartbeat if I weren't also buying a bunch of useless mana), and I don't think anyone should have to.