Make an MS class into a league champion.

Shadower.

Passive: Fake. (Passive) The Shadower has an 5% chance to dodge basic attacks or take 15% reduced damage from an Area of Effect skill. The Shadower will gain 25% movement speed for 10 seconds after he Fakes.

Q: Shadower's Instinct. (Passive) After using a basic attack or an attack skill, the Shadower gains a Killing Point, maximum of 5. (Active) Pressing the skill key will give the Shadower increased Attack Speed, Attack Damage, Armor Penetration, and Critical Chance depending on how many Killing Points he had when Shadower Instinct was activated for 5 seconds. If the Shadower is out of combat for 10 seconds, his Killing Points will disappear, one every 5 seconds (unless he is stealthed).

W: Boomerang Step. (Active) The Shadower temporarily blinks out of view, dashing towards the cursor and returning to the cast point dealing damage going forwards and coming back, stunning all enemies at a (20/40/60/80/100)% chance for 2 seconds.

E: Shadow Partner. (Active) The Shadower summons a copy of himself that mirrors his every movement and attack with reduced damage. The Shadower can activate the ability again to make the clone split off, drawing aggro and taunting nearby enemy champions for 2 seconds.

R: Assassinate. (First Cast) The Shadower temporarily hides himself for (5/10/15/20/25) seconds, gaining 50 movement speed for the duration. (Second Cast) The Shadower emerges from his stealth, striking an enemy champion for (100/210/320) damage 3 times, critically hitting on the third strike. Assassinate will do 30% increased damage if the Shadower has 5 Killing Points.

 Spoiler

Possibly incredibly OP. Obviously an AD assassin. pineappleing scary ganks.

That is really extremely OP, not just possibly, it just is. First off his damage is pretty insane with 3 steroids. Then he has 4 seconds of ranged AoE hard cc. He's really mobile with his passive and ultimate. He has long stealth. Think, Evelyn with a superpowered stun with the killing power of Riven on steroids. Tone down the CC to 1 second and the stealth to a maximum of 3 seconds and it's more balanced at least... I don't know, I'm no expert . Or balance him with extreme energy/mana costs and cooldowns