Kingdom of Heaven

Baudouin IV, 1178 - the Leper King versus Saladin, and the clock is part of the challenge. Setup tip from the wiki: set Conquerors Frequency to None so Saladin doesn't get the conqueror trait. Jerusalem out-earns the Ayyubids at the start, so recruit men-at-arms hard (crossbowmen especially) and marry your sister to a heavyweight ally - Hungary and Georgia both work. Then bait the war: declare on something adjacent, wait for your ally's stacks to arrive, and break Saladin's armies decisively. NB: at the Roads to Power launch there was a Paradox-confirmed bug where beating Saladin didn't unlock this (the in-game menu even showed it unavailable); if the achievements tab in your campaign says it can't be earned, start a fresh save rather than pushing on.