Cut off the Head... and the Body will Follow
Ultra rare0.4%ObjectiveOptionalSingle-player
Successfully use the Eradicate Casus Belli against a House that you have a Feuding Relation with
Needs All Under Heaven. Two stages: first manufacture a FEUD - keep murdering one house's members via schemes and events until the Feuding house relation forms (an intrigue build accelerates the grieving process, so to speak) - then declare war with the Eradicate CB against that house and win. The wiki's one tactical note: pick a house outside any Bloc, so the war stays a private matter.