Ever try running down a low health enemy with Amumu while your bandage toss is on cooldown? Not easy. The combination of Boots of Swiftness and the Rylai's Crystal Scepter makes the prospect much easier to do. This will allow you to either tantrum your enemy to death or let your team catch them easier to kill them.

At the end of the game where chasing people becomes less of a prospect to deal with exchange out your Boots of Swiftness for Sorcerers Shoes for that extra magic penetration.

You can also exchange one of your defensive items (thornmail if the threat from ad is low or force of nature if the threat from ap is low) for a void staff to get even more magic pen.

If you find you are dealing with too much cc investing in a pair of merc. treads is not out of the question.

The real joy of this build is that the build itself covers everything in a general sense but also leaves itself open to being altered for any situational needs that may arise.