Some mechanics which would set him apart could be a TW:WH style Martial Prowess where he has buffs to power and maybe stamina while at full health and as he takes damage he loses these stacks. Temp Health would not recover these stacks but carrying a tome would grant him passive health regeneration, perhaps at the cost of being unable to equip healing items once picked up.
I would also like to see him get a bonus while holding a grimoire, maybe even an inability to use potions in return for 100% curse resistance? As for his ultimate I’d like to see him empowered by a prayer, perhaps taking time to actually say the prayer, similar to the length of reviving a player, and gain increased damage reduction and a ton more power. Exchanging attack speed for even more power could make for some interesting talents as well, perhaps making WP an Uber specialised Elite Killer with little horde clear.
As for weapons, a more powerful and slower version of Sienna’s mace in hammer form with the ability to reverse the grip to use an armour piercing spike would be a very unique weapon. Also a prayer book or two with the ability to shoot a beam staff or flame storm esque wave of lighting or blinding and burning light. Would a Mjolnir esque throwing hammer be too far? Essentially Bardin’s throwing axes but able to consistently 1 shot specials and elites and with less speed.