By slipping into the enemy's land

A scout reports that the Prince-Bishop's army is camping at the edge of his lands, having not yet set out. This army was composed mostly from the lower classes, people who neither had seen battle before nor even owned their own weapons. You were confident that this campaign would be easy.

During both war and peace, Eisheth was your greatest asset. The demon had so far proven to be entirely loyal, more importantly, she was immeasurably powerful. The power of most of the demons came from their physical form; Minotaurs, with their hulking size, were stronger than any man; Nymphs, with their nature-like looks, could ambush any foe; Harpies, with their wings and talons, could appear out of nowhere and tear a man to shreds in a matter of seconds. But Eisheth had magically powers greater than you could ever comprehend, and she would be your greatest weapon against the Prince-Bishop and all other foes you found yourself against.

Eisheth was unable to teleport your entire army to the Prince-Bishop's realms, but she would be able to bring across a small vanguard. You selected from your ranks a handful of demons of different breeds, a Kelpie, a Minotaur, a young Drider, etc. You were unsure which talents you would need so you made sure that the vanguard was as diverse as possible. You grab a bag containing rations and your spellbook and kiss Cecelia - who would be ruling in your absence (her suggestion) - goodbye. With everything in the village in order, Eisheth utters the spell. The whole world around you vanishes, then the trees of a forest in the Prince-Bishop's domain appear before you.

A nymph, one of the scouts you sent into the area, greets you. You follow the nymph to the edge of the forest where you see the Prince-Bishop's army camping in the distance. The nymph reports that there are approximately 2000 fighting men, and another 1000 composed mostly of stable hands, engineers and surveyors, and camp followers. You have 20 demons with you currently. No doubt your demonic army would obliterate this human army in a pitched battle, but then the whole world would know that you are a lord of demons. It would be best to try an alternate way of dismantling the army, lest the entire world learns of your power and joins battle against you.

You order the Kelpie, a sort of nymph that swaps between humanoid and equine shape, to take horse form. You mount the steed and ride off towards the encampment, the rest of the demons following close behind. As you get closer you see a walled city past the army, with a mighty cathedral on a hill looking over the city. You notice that something feels off and this feeling gets stronger the more you approach. The Kelpie feels it too, you hear her grunting and shrieking, and suddenly the beast rears up - you try to hold onto her but you fall off smashing into the ground.

When you get up you see the Kelpie has reverted into human form and was vomiting. You look behind and see almost all of the demons had stopped following you 100 meters back, only Eisheth had caught up and she looked deathly ill.

"O Creator, please allow us to leave this place, something dreadful is afoot."

You lift the Kelpie over your shoulder and rush as fast as you can away from the cathedral. You arrive at the other demons, all of whom look sick. Can demons even get sick?

"What magic is this!?" you ask the demons.

"Someone has erected a barrier against our kind" replies one of the demon.

"Eisheth, can you disable it?" you ask.

"Forgive me Lord, for I cannot. 'Tis a strange magic here, my very being is repulse'd by it."

"If my army were to fight the Prince bishop's with this magic active, we would be slaughtered, wouldn't we?" Eisheth nods. "Is there a way to stop it."

"Methinks it certain. Though, Creator, thou might slip inside and break the spell, then we demons may enter the city unhindered."

You think it over and conclude doing so would be the best course of action. You consider yourself lucky you brought some rations and the spellbook. You feel naked without Eisheth by your side, this would be the first time you were separated from her since the night you summoned her. The demons retreat to the forest while you alone walk towards the city, unsure of what you will find.