One-Way Window

[Prethen]

I never really noticed this magic item previously in the ACG and I got to experience it first hand as a GM. I have to say wow...for players this is extremely powerful.

As a GM, it can sort of wreck scenarios with the fact that it can be used an infinite amount of times per day. The players put it on every wall, the floor, the ceiling, wherever. There's no mystery left to where they enter (assuming the walls aren't too thick and they have darkvision if the space beyond is dark....and I'm assuming darkvision works here and that's what I allowed in my last run).

I realize that gloves of reconnaissance are similar but at least they have limited uses per day and only the player using them can see.

Used in this scenario...:

#3-15: The Haunting of Hinojai; the entire house and every floor (through the floor and ceiling) were an open book to the players, including Dagagal and the BBEG just waiting for them.

[robertness]

Remember, this is a cursed item. It's exists to make your characters' lives miserable. Look at the text of the item, especially the second paragraph:

Cursed Items wrote:

However, once the owner of the window uses it to spy on hostile creatures, its curse activates. From that moment on, the window presents its owner and anyone looking through the window with an artificial image of the other side designed to lull them into a sense of false confidence—enemies appear sleeping or drunk, pits have obvious plank bridges for easy crossing, and so on. While presenting this image to those in front of the mirror, it reveals those viewers to the enemies being observed, creating a two-way window; however, viewed creatures see those using the mirror accurately and can read their thoughts as if using detect thoughts. Furthermore, the image shown to those using the mirror does not reveal that the creatures they are watching can see them as well. Once the curse activates, the owner comes to regard using the mirror to spy ahead as his most effective tactic (after all, it has no limit to its duration) and does so whenever possible until curse-breaking magic frees him from its influence (anyone who uses the mirror to spy on hostiles, even if he wasn't the one to activate the mirror, is also subject to this desire to continue using it).

My interpretation is once the character uses it to observe hostile creatures and until she pays to have the curse removed (which needs to be resolved by the time you pass out chronicle sheets), they're essentially walking from one encounter where the NPCs all act in the surprise round to another. Or whatever devious situation that NPCs who are fully aware the PCs are coming and what they're thinking can come up with.

[Sebastian Hirsch]

Yeah wall thickness seems to be the deciding factor here, but remember to let the group make stealth checks, if they are close enough to use the item, they might be close enough to get detected.

Frankly most scenarios don't go into a lot of details here, and even without that GM discretion, there are certain scenarios where the item will be of little use.

@robertness, the item from the Advanced Class Guide includes no curse

[andreww]

As one of the players in said game wall thickness could be an issue, although probably not in that particular house. I would say that there is no way any of the enemies in that game would have been unaware of us. While I havent read the scenario I would totally have had the end boss attack us while we were busy with the skeletons or at the very least have multiple extra buffs. Tactics only go so far, PC actions can and should change how NPC's react unless their is something explicit in the scenario. Given my -15 stealth score we weren't sneaking up on anyone.

[Prethen]

I'm not sure, functionally, how the window would work differently than the gloves as far as detectability. I don't think the characters are any more noisy moving around a room than they might be when they carefully (an assumption, of course) placing the window on a wall/floor/ceiling. I don't think the NPC strategy would be any different in most cases. In the case of this particular scenario, I don't think there was any reason/chance to change how it was written.