Minecraft wiki entry for Magma_Cube, associated text: The maximum of magma cream can be increased by 1 per level of Looting. Looting 1 averages 0.5 per kill, Looting 2 averages ~0.81 per kill, and Looting 3 averages ~1.21 per kill. Unlike a lot of common loot which picks a random number between 0 and 1 for its drop, the magma cube's drop ranges between -2 and 1 instead. This leads to the 25% drop chance from an unenchanted kill, as well as the relatively low averages with the Looting enchantment since a negative base roll can cancel out the bonus roll made by Looting.