Level 256 gave me a headache. Perhaps I'am not the only one and there are others around, who have difficulties solving it. So I want to share my approach.
Certainly there are other and better ways to defeat the enemy. Here is mine:

1.The setup:

2. Bring enemy heroes to the first line.

3. Kill enemy Hiru first with a Erys & Torr attack, because his explosives are threating.

4. With luck Huron & Kiit hit the enemies. If the enemy Mori survives, you probably have to invest 1 move to get your Erys out of the line of fire.

5. With 500-600 HP left and healthy heroes you can withstand the second wave. Maarrar in the first line is no threat. Better the enemies with 200HP die before they get the immense extra health. In this example I was luckless. But even with the extra health it's possible to defeat them.

Good luck.