From AmtWiki

From the Rulebook:

This State has both offensive and defensive purposes and greatly limits a player’s ability to interact with play. Insubstantial players:

  1. May not move from their starting location unless otherwise noted. This is different from Stopped in that you can still move your feet.
  2. Are incapable of physically interacting with game items, objectives, or other players in any way unless otherwise noted. This does not prevent you from retrieving equipment.
  3. Can only be affected by mechanics that work on States in general (such as Release) or Insubstantial in specific (such as Dimensional Rift). Player and their carried or worn equipment are otherwise unaffected by combat, magic, etc.
  4. Are not affected or stopped by game terrain such as walls, lava pits, traps, etc unless otherwise indicated by the reeve or game designer.
  5. May be seen and heard.
  6. May see and hear.
  7. May Charge abilities.
  8. May not target others unless otherwise noted. May only target themselves with magic and abilities that are able to affect insubstantial players.
  9. May remove this State from themselves at any time by Incanting “I return to the physical world” x2 provided they are the cause of the State and entered it voluntarily. Otherwise they must end the State as per the description of the responsible Magic or Ability.
  10. The ending Incantation for Insubstantial is not interrupted by the player moving their feet, and does not require a free hand.
  11. Insubstantial triggered from enchantments worn is not considered voluntary.
  12. Must indicate their Insubstantial State by saying “Insubstantial” if asked, attacked, or targeted by a Magic or Ability.
  13. May not delay the game excessively. For instance, you may not use the Insubstantial State to avoid being killed if you are the last player alive in a Mutual Annihilation battlegame. The reeves decision in these situations is final.