Iron Slug

Iron Slug is a giant, shiny boss consisting of Diamond, Gold, and Iron. It's eyes glow with a brightness of 12. You must have ten of every underground ore/ingot in order to fight it. This means that you must have ten coal, iron ingots, redstone, gold ingots, diamonds, and with the exception of three Emeralds. It will appear when you have all of these things in your inventory.

Tactics
The Iron Slug is actually partially transparent, meaning that you can see through it. It can teleport around every two seconds, and you must hit it within that time. The Iron Slug's skin serves as armour, which is equillivant to a diamond helmet, gold chestplate, and Iron everything else. It will try to teleport above you and squash you flat with it's massive frame (10 blocks long and 4 blocks high). It does have low health, with only a laughably 30 <3, compared to other boss mobs. When you kill it, it will drop its own armor (listed above), along with ten diamonds, three gold ingots, and 20 Iron ingots. It is very resoursefull, as it can easily be challenged again once you find 6 more Iron Ingots from undeground.