Sanctuary – “Life in death and death in life” [Campaign 4 – Mission 4]

Do you mean in the mine? That is, near the castle?
Well, I'm playing on easy difficulty, and I was defeating all these guys with a combined squad of 37 Kappa, 5 Priestesses, and 45 Sharks (the Sharks weren't always used).

Tyangbo learned a cool spell from previous missions, I don't remember the name - "Slippery Puddle" or something. It creates a 3x3 icy surface that slows down the enemy + damages them with icy icicles.
In this puddle, they lose 3 turns while crossing it, the Kappa has time to jump, then move back and jump again + the hero's direct attack. + one more "Flash" spell at the end.
They all die, and I have no losses.
And with Kappa archers, it's even better) they attack in an area =)

Added 1 minute ago
Ah yes, I used the "Ice Block" spell on the Yuki so they wouldn't shoot.