Emerald Ore
As the drop of the rare field monster, the blue slime king, emerald ore is quite valuable in terms of crafting. Much like slime crystal, Emerald Ore is a more explicit form of ore that is able to be crafted into weapons and armor, but one notable aspect of it is its latent ability to utilize elementals. During the beta, it was highly valued yet very broken, as emerald ore was the only material to be able to use elemental-based powers. This latent power was removed in the official release, but with the Will of Mimir patch, it has been designated as the wind elemental, which can be very useful when fighting dragons to protect against their fire, along with multiple new ores that will represent the other elementals included in the patch.
Even when its latent powers aren't being utilized, Emerald Ore-based equipment are very powerful, representing mid-game level armor and weaponry, only surpassed by items dropped in the upper 20's and beyond in terms of strength and value. Armor crafted from Emerald Ore would be unable to utilize the latent powers no matter what,but it is still very effective at providing a staple defense, and offer protection from the early ruins to a large degree.
When the latent powers are embedded into weaponry, players can activate skills to utilize the elemental, which runs off a charging system. The more used, the longer it takes to replenish the elemental within the weaponry. Summoning wind-based attacks, any weapon embedded with emerald ore can bring the upper hand in a dangerous battle in favor of the player.
Other uses of Emerald Ore is still unknown, as no one has been able to obtain any in game yet, but other applications will be made clear as they are discovered by the playerbase.