Empty Body is a Monk feature gained at level 18 in D&D 5e. Beginning at 18th level, you can use your action to spend 4 ki points to become invisible for 1 minute.
Beginning at 18th level, you can use your action to spend 4 ki points to become invisible for 1 minute. During that time, you also have resistance to all damage but force damage.
Additionally, you can spend 8 ki points to cast the astral projection spell, without needing material components. When you do so, you can't take any other creatures with you.