Minecraft wiki entry for Levitation, associated text: Levitation causes the affected entity to float upward at a rate of 0.9×level blocks per second. This does not affect swimming or flying. Negative levels cause the entity to float downward, overriding the usual falling due to gravity; level 0 (amplifier 255) makes falling, jumping and ascending stairs impossible. When damaged by a projectile or anything, this makes the player go higher in the air on level 255.