Magval eggs form deep in a volcano's magma chamber. A few eggs make it to the surface carried by lava flows during eruptions or brought back by daring cave explorers. However, most eggs remain underground.
After hatching Magvals move out of the magma chamber and into the lava tubes. Here there are plenty of minerals for the young Magvals to eat. As Magvals grow larger they begin to carve their own tunnels, eating most of the rock as they go. Much like their cousins, the Ignalts, Magvals grow very slowly and will continue to grow in size their entire life. Once a Magval become too large to move easily though the lava tubes it makes it way back to the magma chamber where it joins the greater Magval colony.