Cooldown Reduction
One thing that's been bugging me lately is cooldown reduction, and the changes to The Black Cleaver are sorta pushing me to make this thread. Specifically, my distaste is with how it works for mages.
Right now, one of the things that makes tanks so strong is the average tank build has the perfect balance of stats. With masteries (and possibly runes), plus the extremely powerful Frozen Heart (lots of armor, CDR), and either a Spirit Visage or Locket of the Iron Solari (lots of MR, CDR), you're looking at a perfect balance of tanky stats plus an easy 40% cooldown reduction. It doesn't even matter what items you build, because they all contribute towards having Feast up every 48 seconds or Unstoppable Onslaught every 36 seconds.
With the new Black Cleaver, that's another option for a lot of tanks or any kind of fighter. But what's worse is how it means AD casters and assassins now have even more versatility in their kit. For your assassins like Zed and Talon, having a Youmuu's plus Black Cleaver are going to alone give 30% cooldown reduction, on top of basically ignoring any armor on their target. If you add masteries, possibly runes, or any other item like Zephyr into the mix, it's another easy 40% cooldown reduction.
But what about mages? Their only "core" item that has cooldown reduction on it now is either Morellonomicon or Athene's Unholy Grail, both of which feel like wasted item slots. And before you start hating me for saying that, I want you to consider the following: no matter how far ahead or behind you are as a mage, those items aren't just there to boost you, but are almost mandatory. You have to focus your first 2300/2700 gold on just keeping up with champions like Cho'Gath or Zed. You can't say "man, I'm ahead, I'm going to rush this offensive item that gives me CDR" or "man, I'm behind, I'm going to rush this defensive item that gives me CDR". No, you can only say "man, I need to rush this item that keeps my mana pool high enough to trade with my opponent, that also happens to give me CDR".
And then what? That 20% is about it. Not only do you only get 5 item slots compared to most champions' 6, but you're going to be left with 25% cooldown reduction (20% from AUG or MNC, plus 5% masteries). Theoretically you can grab Twin Shadows or something else. But those aren't core. Those are gimping your damage even further. So while that Zed's 2-item build is giving him 40% CDR, ignoring 36% (+20) armor, and adding to his damage, you're sitting there still unable to clear minion waves with a single Lucent Singularity or Orb of Deception because your 2-item build is all about keeping you in lane for more than half a dozen spell-casts. While Cho'Gath already has 3500 health and 160 armor, you're still basically only working on your first actually helpful item. That Sion's dealing more damage than your AP carry because his base damages coupled with 40% CDR are putting out as much burst damage as your full-build Syndra.
On top of all that, mages get fewer options in other areas as well. If you want CDR from Glyphs/Quints, you relinquish AP, which again means gimping your damage. If you want Lucidity Boots, you relinquish Sorc Shoes, which is a huge trade-off for damage. There are so many routes for mana regen, but all of them are redundant when Morello/Athene's are mandatory. Half of the stats on Tear of the Goddess are wasted, half of the stats of Elixer of Sorcery are wasted, I could use mana regeneration Seals but that would be a waste.