Ethereal

Ethereal (sometimes called Ghost or Decrepify) is a type of status effect that makes the target immune to physical damage while also being unable to attack. Afflicted units can still cast spells, but will also take 40% additional magic damage.

Ethereal abilities are excellent counters to heroes which rely on their auto-attack to do damage, such as Ursa and Anti-Mage. It can also be used in order to maximize spell damage against specific targets. Additionally, it can be self-cast in order to block physical damage at the risk of taking extra magical damage.