This card is a great challenge for any judge to deal with. The key part to remember for judging this card is that the realm is first played, and then it can imitate the power and world of another realm in play. Therefore, it wouldn't work to let the realm be played immediately even if Menzoberranzan (1/4th) weren't banned on the card (I think that was just done for clarity).

For the same reason, powers that activate only upon being played (like the Temple of Elemental Evil (124/1st) or Furyondy (122/3rd)) are worthless to imitate, because the Land of Legends is already in play. Ancient Kalidnay (92/AR) and Avanil (5/BR) were restricted because of speed issues. It is also very important to note that it can only imitate opponents' realms, so it is only as effective as your opponents are (especially since razed realms for the most part are considered to have no special powers).

The question of when to play this realm is a tough one, as by the time you have a good realm to imitate, it will be well back in your formation. The best time to use this card is immediately after playing Siege (203/1st), into the front place in the formation and imitate the opponents' most defensible realm. However, this is the best combination you can come up with this card, as when you imitate another realms power, you also take on its world designation, so it's near impossible to have a holding ready to attach to it.

Finally, remember that even if the copied realm is razed or removed from play, the Land of Legends keeps this power until being removed from play.