Levitation

Levitation causes stuff to levitate.

Effect
Causes the affected entity to float upwards at a rate of 0.9×level blocks per second. Does not affect swimming or flying. Prevents the use of elytra, but the effects do not show if the player is already gliding. Negative levels cause the entity to float downwards, overriding the usual falling due to gravity; level 0 (amplifier 255) makes falling, jumping and ascending stairs impossible. Fall damage is not affected.

Immune mobs
No mobs are immune. However, mobs such as shulkers suffer no actual effects.