User blog comment:DamonDraven/Some AS Items Overhauled/@comment-35229418-20141213130332

One post as a response for everyone that is puzzled and/or concerned about Runaan giving CDR: my goal is to give it a specific purpose, which is being an option for Teemo, Kayle or AP Varus. Coupled with Nashor's it reaches 30-40% CDR depending on masteries and runes, which does make sense for those 3 (more ults/W procs for Varus, more E uptime/Rs on Kayle, more MS boosts/shrooms for Satan) - but they would fill a slot with an item that doesn't grant AP, so it's a kinda fair trade.

It's true that CDR isn't of much help on ADCs - but, well, let's be honest, it's not like Runaan is a good item on them anyway. Maybe as a sixth item, but then you wouldn't have any defenses, so yeah.