My memorable percentile moment came not with a 00, but with a 01.
The party was on board an airship floating above a city that was being overrun with monsters. The monsters were issuing out of a gate which the PCs were unable to close or destroy. As they watched on, helpless, I asked if anyone wanted to do anything special. The cleric in the party stated that she prayed for the city's salvation. I thought to myself, "sure, why the heck not?" So I told the cleric's player to roll percentile dice.
"Oh, shoot," she said. "I got nothing."
I asked her what she rolled.
"01," she said.
That was what she needed for divine intervention, an old house rule from the first AD&D game I ever played in. So we took a short dinner break while I figured out what happened. In the end, I decided that the clouds parted and a beam of positive energy shone down from the heavens, smiting the gate and the tower it was in, utterly destroying them. The area became permanently
consecrated and in time, a shrine to the cleric's goddess was built there. I wanted to put a statue of the cleric there, but the PCs were working undercover for the government and were very clandestine about their activities, so nobody knew who she was.
