[FAJ]

Yomi get no sacred troops, no high armor and have expensive casters. Aside from bandits, the average armor is 4 on them; they have average skills and cost a lot of gold.

AoE damage spells and massed archers put down oni in droves. You can try banishment, but I have never seen it do any real damage. Flaming arrows isnt necasarry, but it will solve all your Oni problems until he can cast arrow fend.

Wither bones is nice too, it can wipe out the oni spirits.