Unique passive: take 10% reduced damage but deal 10% reduced damage

Yeesh, 10% flat reduction might need changing. Maybe something like: When you auto auto attack a champion, you gain 10% resistance to damage, but lose 10% of damage dealt by you for the next 5 seconds.

Cooldown maybe 30 seconds?

The ones who would pick it up probably won't be the ones with high base damage to begin with so that's not really a good trade off.

Uhhh, interesting concept but it needs tweaking, Consistently having damage reduction would be broken af

Maybe as an active that had a decent cooldown and only reduced champion damage

Otherwise it'd be pretty busted