Tahm Kench and the Invincible Creatures.

So I am not sure if Riot or anyone else knows this, but there is a Glitch with Tahm Kench when he eats a minion or any type of creature (doesnt work on champions.)

Essentially all you need to do is spam your Devour ability as fast as possible.

Not only will the enemy not take any damage but it makes them invincible. You can still target it with attacks but it will take 0 damage and cannot be killed. The only way to fix it is by eating the enemy again and not spamming Devour.

It worked VERY frequently to the point there sometimes I unintentionally give the enemy a minion that never dies and they end up destroying a wave of minions all on its own.

Edit: There is a higher chance of success if done on a minion with almost no HP left. Simply eat them before they die and immediately spit them at a wall or other minions. After a few tries you will see the minion remains as 1 hp and doesnt die.