Riot, for some bonus creativity, here are some unique abilities

Ability 1 : Champion Q (For some reason I really like the letter Q) places a mirror / Magic Reflective Surface (Don't question it JUST YET) at a location for X number of seconds that can take Y amount of damage from basic attacks or Z abilities reflected. When placed it can reflect all abilities based on the angle they hit the surface on.

(Ex. 's Kame Kame Kame Kah (Her R) hits it at a 45 degree angle, going from left side of map, and is reflected at a 45 degree angle to the top side of the map. The total angle would be 90 degrees, making a right turn. The way it would interact with boomerang abilities would be to reflect it when it reaches the mirror and when it reaches max range returns to the champion that threw it.) (Gameplay mechanic, kill enemy adc with the mid laner's skillshot, or literally make the enemy kill themself with their ult.) (Doesn't work for ground targeted skillshots unless the positioning of them is somewhat of a line. Ex. Q)

Ability 2 : Champion M (For Miner) permanently destroys a part of terrain. Can only be used on interior walls. Does not work on base walls. (Small amount to prevent literally making a strait line from red to dragon, can create interesting game mechanics such as allowing an allied to go through a formerly impassable wall) (If not able to go through a wall, then it makes an indent in it)

Ability 3 : (Passive For a Banker Champion, weapon of choice : Money Pistol) Champion B (For Banker) gets an extra 4 gold/10. Champion B loads his gun with his own money, spending 1% of his current gold every basic attack and dealing bonus physical damage equal to 2x that amount.

(SHUT UP AND TAKE MY MONEY!) (Gameplay mechanic forces champion to recall earlier for components, make decisions on if building attack speed is worth it for the bonus from passive if it drains your funds.) (Ex. With 4K gold you deal a bonus 80 damage on hit and consume 40 gold. Might need to have numbers fine tuned.)

Ability 4 : Champion N (We don't have a champion that throws needles) roots himself / herself until reactivated or X amount of seconds. (Scales down with attack speed) During this time, he/she puts extra needles in between her fingers. On his / her next attack, next 2 if 5 - 7 needles he / she throws 4 needles, dealing bonus physical damage. If he/she channels long enough to have 8 needles ready, then on his/her next attack, she jumps at her target throwing a flurry of needles dealing (70/80/90/100/110% of base AD) (200/210/220/230/240% of bonus AD)

(Balanced because of high cooldown and high mana costs.) (Numbers will probably need some fine tuning) (Minimum needle reload time of 1 second) (Riot I am trusting you to math this.) (Long reload time with no attack speed for burst damage, or build attack speed for less burst but decent reload time.)

I have spent around 40 mins on this post, I think I am done for right now.