Balance Idea's: How to balance Spear of Shojin.

One way I would ensure that Spear of Shojin can be balanced and geared towards Bruisers. Make Spear of Shojin have a Damage reduction cap of 33 but that cap increased by one per 100 HP.

UNIQUE Passive: Reduce damage from champion attacks and abilities by 20 plus 10% of bonus attack damage (maximum 33 + 1 per 100 Bonus HP)

So if you want to more damage reduction, then you have to build some durability aka bruisery so champs like can't get insane gains from it.