minecraft-assets/assets/minecraft/advancements/story/form_obsidian.json

{
    "display": {
        "icon": "minecraft:obsidian",
        "title": "Form obsidian"
    },
    "parent": "minecraft:story/lava_bucket",
    "criteria": {
        "obsidian": {
            "trigger": "minecraft:inventory_changed",
            "conditions": {
                "items": [
                    {
                        "item": "minecraft:obsidian"
                    }
                ]
            }
        }
    }
}