IMHO, i see people, even MLG pros on their stream, neglecting the true potential of kassadins ult with CDR.

its a longer range flash, on a 4.5 second cooldown that does high damage to the area. the outplay potential is insane, you cannot catch him, you cannot chase, and never, will you EVER escape his purpleshwartz pimpslap of dooom.

additionally, as fights go on, its damage output grows, excluding the oretically infinite damage inflation over CS/time mechanic of Nasus Q, or the AP from veigars Q. with a few stacks on it kassadins ult has the highest base damage of any ability in the game...on an AOE, flash... out of nowhere.

i cannot stress how amazing it is.

i find that this build has just the right mix to keep you alive and a constant, near global threat.

ult over a wall into teamfights, combo, then back over the wall, only to re-engage with your full combo again, often unexpectedly from seemingly nowhere, only to vanish, leaving a dead, high damage squishy in your wake.

the CDR allows you supreme control, the mana pool allows you to keep going even after your ult has several stacks and a prohibitively high cost (and extreme damage)

pros, amazing mobility, utility, survivability, great DPS and CC near constant silence (silence lasts 2.5 seconds Q cooldown is aprox 4.5 seconds . considering typical missile travel time, your target has only 1.5 second openings to cast spells) and ult stacks allow for high damage regardless of AP.

"cons", not much AP until relatively late, requires map awareness, reflexes, timing and positioning expertise. requires ult stacks to truly "burst"