Leader: Urban II
Special unit: Crusader (Knight replacement that does extra damage when fighting in the land controlled by infidels and adds religious pressure on victory)
Special District: Holy See (Holy Site replacement that adds full adjacency bonus, costs half as much and generates gold, science and culture equals half of their faith output and shares functionality of encampment)
Your city center generates prophet points so you are pretty much guaranteed to get a prophet (There's probably better ways to handle it, but harder to reconcile with Saladin).
You get bonuses to religious pressure.
Anyone who shares your religion is forced to be your defensive ally. If city-states who share your religion is dragged into war against you, they'll wipe out envoys as well.
If you are in a golden or heroic age you get crusade casus belli that forces everyone with shared religion to participate.
You get +1 envoy in any city-state that shares you religion, and +4 more as long as you are their suzerain already.
You can't produce units in cities other than capital at all, nor can you build any buildings. Any industrial output converts into gold and faith 50/50. You can buy buildings with gold or faith.
Any unit that was built on this turn or bought on previous turn can teleport to any holy site you or your ally of the same faith controls.