Obsidian Bucket adds an obsidian bucket and disables the ability to pickup lava with an iron bucket.
The obsidian bucket acts exactly as you'd expect from a vanilla bucket. It can pick up and place down any fluid.
If you attempt to pick up a lava block with an iron bucket, the bucket will break and you will take fire damage.
You can craft it with 3 obsidian. Like a vanilla iron bucket.
You get an advancement for breaking an iron bucket, that's neat.
You also get an advancement for crafting a obsidian bucket
The vanilla "Hot Stuff" advancement (usually for picking up lava) is now unlocked by placing down lava with any bucket.