Originally Posted by DRkid
Not every mechanic in the game has a direct counter. True damage has no real counter in this game its just something you have to learn to deal with.
True damage however, is limited in most cases.
Darius's being the prime example, he needs max Bleed Stacks in order to get the most out of the ulti.
Vayne needs 3 shots on the same target to proc her true damage.
Zyra's and Kog'maw's require them to die.
Irelia's is a small boost to her auto attack (which is timed).
Corki gets 10% of his damage as true damage per AA (which is rare when it's more then 80, and that's with a crit mind you).
Cho's feast also has a second utility to it, encouraging it's use on minions rather than enemies.
And Nunu's only hits creeps.
Out of 100 champions, these are the only real true damage in the game, all of which have prerequisites in order to effectively use (outside of Cho’s ultimate, where half of its effectiveness requires you to eat minions).
Edit: Fixed with Quote