Jagged Edge, the Headhunter
Jagged Edge is a single-target assassin that takes down his enemies by debuffing them while buffing himself with mobility and auto-attack modifiers. Here's his abilities:
Passive - Headhunt - 1 minute cooldown after 2x bonus stats fades Whenever Jagged Edge kills a unit, he gains a stack of Headhunt. For each stack of Headhunt he has, he gains 10 movement speed and 1 armor penetration. This can stack up to 5 times and each stack lasts for 30 seconds. Killing a unit refreshes the timer on all stacks and upon reaching 5 stacks, the bonus stats are doubled for 15 seconds.
Q - Sweep - Active - 75 mana - 9/8.5/7.75/7.25/7 second cooldown after slow ends Jagged Edge swings the dull side of his blade around himself, knocking the first enemy hit behind him and slowing them by 20% for 2 seconds if it is a champion or stunning for 1 second if the target is a monster. He then stabs his blade into one of their arteries, dealing 50/75/100/125/140 damage over 2 seconds. EMPOWERED: The first enemy hit is instead stunned for 1.25 seconds and bleed damage is doubled.
W - Ambush - Active - 100 mana - 45/35/30/25/20 second cooldown after buff ends Jagged Edge gains 5% movement speed for 5 seconds. If he attacks anything, he loses the movement speed, but deals an extra 15/30/45/60/85 damage. EMPOWERED: Doubled duration and power of MS buff and basic attacks critically strike during it.
E - Dead Meat - Active - 50/60/75/80/95 mana - 5/14/13/11/10 second cooldown after debuff ends Jagged Edge marks an enemy, empowering his basic attacks against them for 3 seconds. His basic attacks slow the target by 15% for 1 second if the target is a champion, and ignore 20 armor if the target is a monster. EMPOWERED: Basic attack slow duration and power doubled and 15 armor penetration is gained.
R - Hunt - Active - No cost - 150/120/90 second cooldown after buff ends Jagged Edge readies himself for a major hunt, empowering all of his abilities for 10/20/30 seconds. During this time, his basic attacks against champions grant him 1 stack of Headhunt and reduce the cooldown on his basic abilities by 1 second.
Edit: Much more clarity, ultimate rework, and all around ability changes.
leaves spawn, he has 1100 MS, yours would have 1800-1900 MS forever at that point, only getting larger. So that's the Passive broken as all hell, but what about the other abilities?
, though if it scales off of AD, he could just mash Q on a minion wave to delete all of it, as he is resourceless
passive in every way, giving better invis and speed (which is a bit redundant with his broken as all hell passive), damage, and everything he needs to be everywhere.
passive, except he also permaslows the opponent by walking towards them? It's not bad enough he has 2 insane MS boosts already, now he can permaslow enemies by walking towards them. At least 
has to AA them and use mana.