What's the approximate battle setup?
The army is as specified in the task: 5 Psionicists, 10 Fire Elementals, 8 Earth Elementals, 15 Air Elementals, and a single Butterfly.
I used a hero with 6-6-3-2 stats and expert offense; the only spell needed is Bless.
Setup:

The main idea is to have everyone huddle in a corner, but with the Psionicists sticking out:

Then, use the Psionicists to wait, protect them with the Butterflies, and have the rest of the troops defend. The Griffins attack the Butterflies and take some damage, then they get hit twice, 3 stacks at a time:

The rest of the battle is simple; the main thing is to keep the Psionicists close to the two stacks, so they won't be attacked, fearing a multi-attack, up to the point of skipping a turn.
In this battle, I was lucky with morale; in the first 3 rounds, it didn't trigger, which allowed me to bring out 3 Air Elementals and all the Psionicists:

In general, all the ranged units are lost, and maybe 1-2 Psionicists. It's better not to bring in fewer than 4-5 Butterflies, as they are not good fighters.