Open Door
1d6 + STR, base chance 1/6
Stuck doors (and many doors in an ancient dungeon are stuck) requires a Strength skill check to force open. It is important to get the door open on the first try, because a failed attempt warns any monsters on the other side of the door that there is trouble.
Multiple characters: Up to a maximum of three characters can attempt to smash through a door together, giving each one a separate, normal chance of success all at once. However, they spill into the room and will be surprised if there are monsters within.
Pickle Jar: If a Open Door check fails and the door remains stuck, the next attempt gets a +2 "I loosened it for you" bonus.
A character with +1 STR is trying to force open a stuck door. They roll a 2, and add 1 for a total of 3. They needed a 6 (1/6 chance) so the door remains stuck but now has a 2/6 chance on the next attempt.