This might have been said already, but Warwick's W used to be global (you would hit it and your entire team would get an AS boost no matter where on the map they were) and his E used to not be toggle-able.

At level 11 or somewhere around there Tristana's passive would outrange towers and she could auto them down without minions and without taking damage.

EDIT: Also Leaves were somehow tied to a computer's registry and could be added to accounts that didn't have leaves on them. You could also see how many games you had left at the postgame screen.

Nidalee was OP with the mastery that gave movespeed when you dodge.

I have a rune from the winter olympics that involves toboggans.

loading heimers tower at beginning when he had 6, and unleashing a wave of minion death after a few minutes, oh and one thing people forgot is, heimer period he fails now

you guy know nothing!!! back in the days jax could dodge turrets!

Pantheons heartseeker strike used to be bugged (huge scaling compared to what tooltip said) to the point where you could go mid and use it with his W to full to zero any current mid at level 3. (if you had any extra AD)

Promote used to be OP when stacked and was removed before being readded again later.

Shaco used to be able to solo baron at 15 minutes using auras without much farm.

Buying elixirs at the start of a game used to be OP to the point where a shaco could use the potion, grab red buff with boxes and run mid deceive in and near 1 hit anyone.

People used to be happy to see Teemo, because it meant the servers were up.
Amumu meant the servers were down.

Blitzcrank meant Konami Code.

AP sion was a troll build