league of legends item that increase damage when critical hit
Solution 1:
As of patch 8.11 the only item that increases Critical Damage is the Stormrazor, that guarantees a critical strike for 160% damage (+1% per 1.5% critical strike chance, max 200%). This means that this guaranteed Critical Strike will only do as much damage as a regular critical shot.
With that said, patch 8.11 changed how Infinity Edge works, and instead of increasing critical damage it now grants a passive that converts 15% of critical strike damage to true damage.
Therefore, as of this patch there are no longer items that increase Critical Damage.