Legacy of The Campeadores

Needs Fate of Iberia (far easier with Roads to Power too, which makes El Cid directly playable from the Wandering Exiles screen in 1066). No ruler-designer characters - you must be related to Rodrigo. Play his unique story content through to its end as a vassal of Castille, build power, take your liege's throne, then engineer Valencia: claim any county in de jure Valencia (pick a duchy mostly held by one realm - your realm priest will hand you a duchy claim off the religious differences), take it, and use the Struggle Clash CB to reach the six counties needed to create the Kingdom of Valencia. Create it, rule it, done - and Mio Cid is explicitly designed to combo with this run.