What was the largest in-game surprise you have experienced? In the 5th Edition campaign I just wrapped up, one of my players stated they had a dark secret and wanted me to fill it in. Through levels 1 through 9 I would ask him certain questions about his character. The campaign was set in the Forgotten Realms and the group had spent quite a bit of time in the city of Nesme. Eventually, drow invaded and in the ensuing battle, the player learned he was a drow spy whose memories were manipulated by Tymora when he was resurrected by the party in earlier chapter. He looked at his compatriots in the adventuring party and RETREATED with the drow, as the battle turned against them, back into the Underdark. We spoke after the session and he was perfectly happy letting his character's arc end that way.