Obsidian Shield

The defense on it is minor. The reason to wear it is that nothing shoves you anymore. Once you stop getting bounced backward on every hit you can hold a position, keep a jump arc, and stay on a platform through a swarm instead of being punted off it. For anyone still learning to dodge, that is worth more than the stat line suggests.

The fire immunity is aimed squarely at hell. Hellstone and its bricks burn you on contact, and between that and constant shoving from imps and bone serpents, this removes most of what makes an early trip down there miserable.

It is the first step toward the Ankh Shield, which is one of the strongest accessories in the game and takes a long component chain to assemble. Keep it in a chest even after you outgrow it. It also works with the Brand of the Inferno, where a successful block opens a short damage window.