I created 3 Custom characters and had Lae'Zel and Shadowheart. We attacked Zalk with everything, surrounding him. Save Guiding Bolts for him. They do a lot if hit. Bless is good to enhance attack chances.
Also, use items you pick up to keep cambions at bay. Throw bulbs and such at them. Area effect and they push enemies. I barely succeeded even doing all this.
