Happy Cauldron. Make Obsidian!

A living cauldron wants obsidian, and there is only one way to make it: lava first, then water on top. Two nozzles hang above the cave. Press and hold one, and the liquid pours down. It will never reach the pot on its own — the path of dirt blocks is yours to draw, with a finger, straight across the cave. Made a mistake? Erase a block and it returns to your stack. Get the order wrong, though, and you get trouble instead of treasure. Water in an empty pot freezes it solid. Streams that meet in mid-air turn into plain cobblestone. And lava spilled past the rim melts the ice under the cauldron, dropping it into the dark. 50 levels across five chapters, each with a new twist: bedrock walls, hanging pockets of liquid, falling sand, brittle ice, icicles. The fewer blocks you spend, the more stars you keep. Pixel art, a cauldron with a face, and no timer at all: think as long as you like.