Tactics Treatise - raise morale?

[BB Shockwave]

I easily supressed it on Level 12, you should be able to on level 10 too. JUst use spells like Slow or summon creatures (Ice Ball, Phoenix, Evil Book) to hold off the 3 points of access where the knights can get to you, and while they are busy there, concentrate on the gremlin towers. I used an (almost) all-undead army (werewolves, vampires, ghosts, skeleton archers, plague zombies).