Head Priest of the Earth Daichir:
Strong monsters have been appearing near the Crystal Caverns. You can get Veridan's Soul Stone, Kechi's Soul Stone, and Michaela's Soul Stone when you defeat Armed Veridan, Armed Kechi, and Armed Michaela respectively. When you combine these three, you can get a Dark Soul Stone.
This is the same item that you can get after defeating Earth Wyrm Trasken. So if you can get a Dark Soul Stone this way, I'll consider it as if you've defeated Earth Wyrm Trasken.