The demons created will have a morale cost of 4 and do not fly.
Health and damage are rounded down so a 13/13 will create 6/6 demons.
A character with a maximum health of 1 will create demons with 0 health that die instantly.
A character with 1 attack will spawn demons with 0 attack.
This is a very versatile spell, it can be used to dodge your opponents targeted removal while still attacking, remove flying from a character, split a big creature into smaller ones making it easier to deal with, help take down your opponents morale while giving him high morale cost units and increase the amount of creatures in your defensive or offensive zones in a pinch.
The text in the circle seems to be The Lords Prayer in latin