What is the correct interpretation of the Dark Room card? It says that if you enter the room, then you lose 1d6 actions. We've been playing that if you enter a Dark Room then you need to roll a 1 to leave it, because unless you have a speed potion, you only have two actions and anything more than a one leaves you with zero actions. Is this correct?
For the Dark Room cards, lost actions are carried over to the next turn until they are used up. Remember, there are two actions for every turn. For example, if you used your turn's first action to enter the Dark Room, then rolled a 3 on the d6, you'd lose the second action of your first turn (1 action). Then there would be two leftover lost actions. So you'd completely lose your next turn (2 actions), and have your full two actions on the turn after that.
If you had rolled a 4 originally, then you'd lose your remaining second action, your complete next turn, and the first action of your third turn. We like to keep a die in front of the player with remaining lost actions so they can count down easily.
Is it OK to use a room-rotating potion by declaring the potion then moving into a room and into another and then rotating that room. Is my turn over when I take the second action to move into the second room, and therefore the potion expired before I can rotate the second room?
You can use a potion at the end of your two actions before the next player's turn. However, when a potion is used (declared), its effects are resolved immediately before any more actions are taken. So you cannot declare a potion's target and then move in such a way that the target is no longer valid. For example, it is not allowed to declare using the Potion of Roomturning on a room that currently has no player, then move into that room, and then use the Potion of Roomturning (which cannot be used on a room containing a player) on that room.
If your intent is to prevent a player from following you, it's generally best to rotate the room behind you after you exit it. The Gauntlets of Stoneturning will allow you to rotate the room that you are in, whereas the Potion of Roomturning has to be a room that does not have a player in it.
Does using the Warhammer against the Boulder obstacle destroy the Boulder? What about using the Boots of Stomping against a Lock?
The Warhammer and Boots of Stomping only let you surpass those obstacles. If it helps, think of the Warhammer as more of a crowbar that lets you squeeze by the Boulder, and the Boots of Stomping as only knocking the door open, allowing you to close it behind you.
When you use an item to surpass a monster, does it kill the monster? And if not, can I take it's treasure?
No and yes (in that order). When you use an item to surpass a monster, you simply scare the monster away for a short time. You may then take any items it was guarding. This means that the next player who goes through that room will have to deal with the monster still being there (and might get no items from defeating it).
We ran out of Potions!
The game comes with 11 potion item cards and 13 rooms that have potions in them. It is expected that you will use a few of them before all the potions are revealed, so shuffle the discarded potions when you run out and draw from there. If no potions have been used, then the potion in that room doesn't appear. This has been fixed in the 3rd edition of Dungeon Escape! There were two blue rooms that had potions in them that were meant to have other items.