DM of my trainwreck homebrew pathfinder campaign, and how a nearly-free magic item wiped our party.
The players find a small trinket shop and they purchase the Oracle's Bell, a (secretly) divine item for a reasonable price. Our summoner/eidolon OP cheeser is the one who found it, so he's the one who gets to keep it. More on this later.
In order for them to know how to use the item, I reveal how it works.
>The bell's chime echos 5 minutes into the past from the moment it is used
My idea is it would allow them set up an alarm area around a camp, so if they get jumped or are going to be jumped, I can have the bell ring and they'll know shit is about to go down. It was meant as a more useful alarm spell.
One of my players is like "Hold on, this is a perfect opportunity for me to break the game. We can use this to essentially set up savepoints, if we go into a dangerous room and start getting party wiped, just ring the bell and we'll go back 5 minutes before we went into the room, and this will be our signal to know not to go in there."
This sparks literally 3 hours of "How do we game this item so that we never die" meta-strategy, and I have to retcon the effect so it can only be used to prevent a player/party wipe one time, and then the bell would break. Otherwise, as a simple alarm, it could be used indefinitely. The act of intentionally ringing the bell to prevent a death would shatter it though.
The summoner then proclaims "Fuck you guys, I'm going to use this for myself and not the party," as if his 150 HP at level 7 eidolon-armored quadruple-armed fire-clawed OP self could actually run the risk of dying after I allowed him to play it instead of banning that shit the moment it was suggested.
And thus, the Garden of Betrayal was formed. Half of the rest of the party fuck off into a sideroom and convene a secret council on how best to take the bell from Summoner, for the good of the party of course.