The Iron Slug is actually translucent, 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 equivelent 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 laughable 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 rewarding to kill it, and it can easily be challenged again once you find 6 more iron ingots from underground.