Air + Air = Pressure
Earth + Water = Mud
Air + Fire = Energy
Earth + Fire = Lava
Water + Water = Puddle
Puddle + Water = Pond
Pond + Water = Lake
Lake + Water = Sea
Sea + Water = Ocean
Earth + Pressure = Stone
Fire + Stone = Metal
Air + Stone = Sand
Sand + Fire = Glass
Air + Water = Rain
Rain + Air = Cloud
Cloud + Air = Sky