THE CARD
Name: Tiara of Opulent Fantasy
Set: MSGS
Type: Artifact
San: -1
Special Effect Box: Costs 1-point of Sanity to use. Replace all of your attributes (not Title or Special Effects) of your Current Location with all the attributes on your target's Current Location. If you use a Gate, rotate your own Location card. Flip this card when used.
CLARIFICATIONS
The Tiara replaces your Current Location's attributes with those of an opponent's Location. Attributes specifically include: the Locational Attributes (listed under the card's Title), the Gate Attribute (located in the top left corner), and the Public Attributes (the icons running down the left margin). They specifically do not include: Title, Dimensional Indicator, Region, Subregion, Sanity Cost or Special Effect Box.
Note that the definition of Current Location in the most recent rules is "The Location on top of, and right-side-up on, your Story Deck (includes Locations at which you have summoned Monsters)." You can not use the Tiara upon a Location that someone is walking to. If someone is walking, they do not have a Current Location. For the same reasons, you can not use the Tiara if you are walking.
As long as your Current Location remains on top of your Story Deck, it keeps the Attributes introduced by the Tiara. This remains true even if the opponent you used the Tiara upon leaves his Current Location, or if the Tiara is Buried. As soon as your Current Location is Buried, however, it reverts to its original Attributes (rules: "all cards revert to their natural attributes [when buried]").
QUESTIONS
Q: Can I use the Tiara against someone currently using a Travel Event?
A: Yes. Travel Events are played to the top of your Story Deck, and are considered the player's Current Location as long as they remain there.
Q: If I've already used a Gate at my Current Location, and then Tiara someone else's Gate Location, can I use it again?
A: No. Whether you can use a Gate or not depends totally upon the orientation of your own Location card. If it's already inverted when you use the Tiara, you can't use it again.
STRATEGIES
Finish an Adventure - Can't get that last Gate, Church, Forest/Water Location or whatever other Location Attribute might be required for your Adventure? Just wait until an opponent travels to such a place, Tiara it, and then play your Adventure. This can be slightly tricky because if your Location is Buried, it loses its new Attributes. Thus, you must be short just that one Attribute when you use the Tiara, and you have to make sure no one else Buries the Location. If you want to be super-safe, use the Tiara from an Exotic Location, since they can't be Buried (but that's probably over kill).
Play Cards - Tired of being stuck without a Tome, Artifact or Gate Location? Usually, at least one of your opponents will possess the Attribute you need. Thus, the Tiara can be used to make sure you don't get stuck during card play in a round.
Avoid Phobias and Monsters - If you want to avoid the special powers of Byakhee, Fire Vampires, Rat Things, or other Monsters that depend upon attributes, you can use the Tiara to borrow a safer Location. Likewise, you can temporarily avoid the effects of some Phobias (although avoiding Phobias in this manner is a pretty small win, only truly useful if you're really struck with bad cards).
Make Your Monsters Better - Dholes get better only if you are in an Underground Location. If any of your opponents are Underground, you can borrow their Attributes. Mummies, Skeletons, and Zombies get better if you or your opponent is in a Cemetary. Perhaps neither of you is in a Cemetary, but a third player is. Again, you can borrow the Attribute to make your Monster better.
COUNTER STRATEGIES
There are a few strategies which may be used to make the Tiara less useful.
Typical Artifact Strategies - Steal the Tiara with Mi-go or Thieves in the Attic. Decrease your opponent's Sanity level so that they can't afford to use the Tiara.
Keep Away - A marginal strategy, since it tends to hurt you as well, but once you've learned about an opponent's deck you can stay away from the Locations that benefit him most. Is he using Dholes? Avoid the Underground. Is he trying to finish Lost in the Catacombs? Stay away from Churches.
Nuke the Site from Orbit - If an opponent uses the Tiara on a Location, it's probably fairly important to him. There is little better time to use Location destruction cards. Bury it with Earthquake. Discard it with Cthulhu Rising or the Wave of Oblivion. Force your opponent to leave with a Townsfolk Riot. Note that this is one of the cases where Burying cards is highly useful, because it causes the Location under the Tiara's influence to lose its new Attributes. It's the only way to be sure.