I came up with these stats for the Horned Demon and ran them against Nomad in a scenario game. He died pretty fast though : )
Unit Name: HORNED DEMON
Type: Uncommon Hero
Size: MEDIUM 5
HELLFIRE BLAST SPECIAL ATTACK
Range: 6 Attack: 4
After using Hellfire Blast Special Attack, if this Horned Demon did not inflict a wound, place one wound marker on this Army Card.
After taking a turn with this Horned Demon, you may choose a common figure within 4 clear sight spaces of this Horned Demon. Roll the 20-sided die. If you roll a 15 or higher, take temporary control of the chosen figure and immediately take a turn with that figure. At the end of that turn, you may destroy the chosen figure and remove one wound marker from this Army Card. If you do not destroy the enslaved figure, control of the chosen figure returns to its previous owner. All order markers that were on the figure’s Army Card will stay on that Army Card. Enslave Soul does not affect psychic figures or constructs.