[Edi]

Against AI, even EA Ulm will absolutely own Yomi. A decent screen of shield maidens (about 50 or so) set on hold and attack, an equal number of archers and then just put warrior smiths in a row with Earth Boots. The first round you hear hat *crump* *crump* *crump* sound of them all casting Earth Power and then the Oni army starts vanishing under a massive barrage of blade winds and magma bolts. I'd typically annihilate armies five times larger than mine with just the shield maidens and the fodder stack in front of them taking losses. Add in priests and banishment...

If your friend is relying mainly on the brute force of the oni, killing him will not be too difficult.

Edi