Season 3 kassadin (Ban rate 99% in Solo Que)
Weedwick (the first patch of the 2015 preseason. The old warwick would oneshots you with R+Smite)
League of cleavers (Just stacking the item as many times as possible)
Ardent meta ( The item gave shielded champion bonus on hit damage, attack speed and a lot of on hit healing. You pick Mage support build this item and then adc turn into insane untouchable 1v9 machines.)
Banner of command meta (Baron empowered cannon creep buffed with banner of command. literally 0 counter-play. people had to save minion demat.)
Tank frizz ( He did a lot of damage with a tank items.)
The most disgusting, unbalanced was Ardent Censer Meta. Champions like Janna, Lulu, Karma and Sona were doing nothing but just brainlessly spamming buffs on their adc. It was literally Speedrunning whos supports gets adc feeded fastest.