How do you get Level 5 Priests?

[Psitticine]

Communion Master/Slave is a set of Astral spells while Sabboth Master/Slave are the Blood magic equivalents. They work the same way, aside from using different power sources, and can even interlink together.

When mages cast Communion/Sabboth Slave, they become "eligible" to support a mage who casts Communion/Sabboth Master. Any spells cast by the Master have their fatigue costs (before skill level reduction) shared out among the Communion/Sabboth. This leads to a tremendous increase in the amount of battlefield magic the Master can cast.

In addition, every two Communion/Sabboth Slaves also grants the Master a +1 to all his magic levels. This allows the Master to cast more powerful magic and suffer even less fatigue damage.

The drawback is that the Master can continue to "share" his fatigue costs even unto the death of the Slaves. The Slaves can be driven past unconsiousness and begin to take injury instead of additional fatigue, especially since they don't get the same reduction to fatigue that the Master will get from his increased power levels from the Commmunion. The spell-casting AI is good about not going to such lengths unless the situation is dire, however.

Note that there are also items that allow the equivalent of a Communion between item-holders.

I'm not 100% sure if this works with priest levels or not. Unless somebody beats me to it, I'll try to play a test game tomorrow especially to test that out. I don't believe it does boost priest power, but I've not specicially looked before.