I think this is the gladiator trophy? Not sure. But if it is…
Start with the dark priest. Use his life drain on the enemies, and inbetween rounds switch weapons to heal your allies. This is by far the easiest one.
Also, there is a glitch, allowing you to get the archer out of the way, which I think is one of the harder ones. While playing as the priest, get to the second last round with as many allies as possible alive. Allow one allied archer to die (just don't heal him before that second last round). When he does, pick up his hat. It will change you to the archer class. Completing the last two rounds will count it as completion with the archer.
Beyond that, the next easiest one is the worker. Just jump a whole lot to avoid arrows, and chuck bombs constantly (don't charge them, it doesn't change the damage just their range).
Really to get past these you have to memorize the pattern of the waves, so that you can take out the important enemies first. Always try to take out priests first, since they heal everyone else. Always jump a lot to avoid arrows and mage spells. Watch out for fire priests – they spell doom unless you get to the water on the left or right really quickly.
Thats about all I got for you, I never beat them all.