Minecraft wiki entry for Combat, associated text: A lava bucket is capable of causing an immense amount of damage to multiple mobs in addition to providing light and greatly hindering mob movement, even more so than water. Any mobs (without fire resistance) that come into contact with lava will suffer 2 whole hearts of constant burn damage every half-second for a total of 4 hearts of damage per second. In addition to that, they will also be set on fire, suffering additional burn damage over time even after leaving the lava. The lava bucket is especially dangerous in confined spaces where it can be used to block off a pathway, preventing most mobs from reaching the user. One should be very careful, however, about where they place lava as that extreme damage figure mentioned above also applies to players.