(We play Death Watch, but that is not central to my question.)
My idea is that the players enter a sentient dungeon that wants them to conquer it and is actively helping them by keeping them alive.
The party is on a timer, and as long as the timer has not expired, the dungeon will "Groundhog Day" them if they make a fatal mistake--such as a TPK or close to it, a vital NPC kill, or a wrong use of perishable items. The players and characters are aware of the timer.
I want this at a cost, though, so when the party is groundhogged, they each draw from a deck of cards. Each card has a penalty, such as -3% to a stat, -5% from a type of roll, or removal of ability (e.g., cannot run or use certain weapons.) or just a blank card so no effect.
I was thinking to have these be cumulative, so if they groundhog a lot, they get weaker, but it takes a lot to make a serious difference.
The idea was that they could fail by 1 on some rolls and think, "oh if only we had not groundhogged that time, I would have got that," and they can slowly discover how to use the groundhog system to their advantage.
Does anyone have experience of a similar system, or advice on how to change it to make it more workable? Does anyone have any guess as the the number of each card that should be included in the groundhog deck ?
EDIT: The dungeon is tied into the groundhog mechanic such as puzzles that can be solved multiple ways giving a key to different door depending on how it was solved.