The ability to make weapons forged with magic crystals.
There are already different kinds of crystals inside of the mines but, only the blue crystals can actually be mined. Different kinds of crystals such as the green and purple ones, (red crystals should be added too) should be able to be mined for different coloured crystals which can be used for the same purposes as the regular blue crystals. From now on, every type of crystal can also be used for infusing weapons with different kinds of magic. Green crystals could have forest magic (nature, found in the forests), purple crystals could have dark magic (found in the mines). Blue crystals could have water magic (found in the mines too, as usual) and red crystals (if implemented) could have fire magic (found in the combat trials or somewhere else maybe). To infuse weapons with all these kinds of magic, the crystals will have to be molten in boiling water or a different liquid to be made an oil out of. The dull weapon part will have to be dipped into the oil which can be kept in anything. After this, that one weapon part will be infused with the kind of magic the oil was made with until broken.