How to get the Crystal Dagger Compared to the previous entry, the Crystal Dagger has much better crit power while still retaining the speed of the former. This is also a weapon that comes as a random drop at the 60th level of The Mines, so you do need to be a bit lucky to find it...
To get this weapon, first, you need to have the Drillbreaker weapon with you. (Mentioned above on how to get it.) For the upgrade part, you need to have a Magitek Core with you for the magic to happen. (They can be dropped by fighting Magitek soldiers or just running and exploring ...