To finish the demo: use the archer for DPS along with the turret, the rogue to clear the marks, the tank to absorb damage, and the wizard to clear the waves. Remember, poison can't hit you, the rogue can't be attacked when invisible, and the level 2 turret is really strong.
It's true that mages are very vulnerable. To avoid getting hit, prioritize positioning near trash cans, as mobs will likely collect trash instead of attacking. Otherwise, I use poison, then void orb to pack the mobs, and lightning to hit in area. The mage is really not to be prioritized.
I think the poison gas is really strong, it never goes away. setting it early at exit and choke points adds up to not just tons of damage but also greatly reduces how often you have to chase someone with trash. let them run, they're not making it
