We Have Struck Diamond is the eighth episode of the original Sky Does Minecraft series.
Plot (see Back Into The Lava Pit)
Sky goes upward to find iron to craft a pickaxe to mine diamond, and he finds himself in a cavern. He finds that the cavern is, like most of his world, very bare, so he mines more. Some lava pors ou many times, and he instantly pulls away from it, boasting about his cat-like reflexes. After a bit more mining, he finds a big patch of diamond. He continues mining, but can not find any iron to craft a pickaxe to mine the diamond.
So...how could he get to the diamond? It's the obvious answer: He needs to start on The Search For Iron.