Could you specify which one?

The author intended to use quicksand again, but since the crystals are faster than the wizards, the tactic from the previous battle wouldn't work. A modernization of the battle was needed. Instead of figuring out how to implement it, I simply used wizards and phoenixes. In the first round, I blocked the liches and put the wizards under fire. In the second round, I summoned a clone. The damage from the wizards was enough to defeat the liches in a few rounds until all the phoenixes died. Then came the quicksand, resurrection of the phoenixes, and finishing off the crystals. As for artifacts, I had to equip the lightning amulet and the medallion (forgetfulness). It's a rather simple tactic, but it worked.