Mythical Diamond

A Mythical Diamond is a shiny purple diamond that looks very similar to a regular diamond. It has no known natural source, for example an ore. Three Mythical Diamonds were found in an Ancient Chest after defeating an Overlord Minion General in the season 2 episode The Caverns of Death. They were later used to craft the Mythical Pickaxe.

Trivia
A Mythical Diamond, as well as the other pieces of the Mythical Pickaxe uses the "enchanted" animation and uses purple text when hovered over, which is very similar to items like the Enchanted Golden Apple.