The wording and behaviour of Time Vault has changed over the course
   of the game, in part to try to clean it up and in part to try to
   control its power level.  The current wording is as follows:

   Time Vault  {2}  Artifact
/ Time Vault enters the battlefield tapped.
/ Time Vault doesn't untap during your untap step.
/ If you would begin your turn while Time Vault is tapped, you may
   skip that turn instead.  If you do, untap Time Vault.
/ {T}: Take an extra turn after this one.

   This uses turn-skipping, which is an extension of phase- and step-
   skipping, to try to limit the number of times the Time Vault could
   be untapped and tapped again in a turn.