Take turns guiding Ember, a glowing lump of coal, and Brook, a bubble of water, through an old mine: Ember wades through lava but goes out in water, Brook the other way round, and purple sludge stops both. Stand one on a pressure plate to hold a gate for the other, throw levers, grab red and blue gems, and get both to their doors. Seven rooms, then the mine again, mirrored. Free, no sign-up — play right in your browser.