Some sugestions to the Patriarch spell:
Overlords: Dreams of the Unthinkable.
When a magic-user casts a spell there is a chance that he gains the Madness promotion. This chance is proportional to the number of overlord cities in the mapand the size of the map. A unit with the Madness promotion can start the turn without any movement point and is automatically converted by Overlord Inquisitors. A unit with the mind, spirit or overlords promotion are immuneto this effect. It costs 10 XP to the Patriarch.
This effect ceases when the Patriarch moves, dies or lose the Patriarch title. As long as the ritual is in effect the Patriarch receives a big defense penalty, -40%, for example. A metamagic spell, probally the Sorcery 3 could dispell these type of "Global Enchantment" for a experience cost equal to the used to cast.
These spell type is a good template to other spells. As a Patriarch Spell it is interesting why it forces the Patriarch to remain inactive, relying in it's assassins to eliminate the competition. The problem with this suggestion is the AI, which I believe is not very good to measure the right time to use these type of big and more or less simmetric effect.
Leaves: Tarrasque.
The Leaves Patriarch gives the ability to all your units to heal in any forest as he was in your cultural borders.
You can sacrifice the Patriarch to Summon a permanent Tarrasque. The Tarrasque starts with so many levels in the nature wrath promotion as there is nature nodes in the map, not counting the nature mana from palaces,and the level of the sacrificed Patriarch. When the Tarrasque attacks it gains power proportional to the number of Nature Wrath promotions it has. Each time he is destroyed it loses a Nature Wrath promotion and is respawned fully healed in the nearest Ancient Forest in your cultural borders. As longthe Tarrasque lives there is no forest grown in the map. Only a Tarrasque can exist each moment. Each time the Tarrasque dies a young forest spawns on the square he died.
With this mechanic the Patriarch keep his mobility, so it is easier to him to keep his Patriarch status and use more easily the Holy War spell. There is a tension between the good bonus of the Patriarch Life and Death. A powerful Patriarch and the powerful Tarrasque.
Veil: I support Wood Elf suggestion, but I think the Patriarch should not die. It could be balanced reducing the number of Balrogs and Armaggedon Counter increase.
I think also each Patriarch should have a different name, for example the Leaves Patriarch should be called Hierophant, and the Order Morning Lord.