Taking over settlements in a territory, garrisoning armies, and many Hero and Lord traits can increase the rate at which Vampiric Corruption spreads. Optimally, Templehof will seize an Empire Province territory outside of Western and Eastern Sylvania, which you should pick as your final target to Subjugate them. The dual-axe berserker variant will chop most infantry like a blender, while the tier-five polearm variant are your most robust anti-large solution. Maybe the quickest way to gain diplomatic relations with allies is to send Heroes to attack and harass the enemies of their allies, since this can be done every turn, and the diplomatic bonuses stack with your chosen allies and the penalties stack with your chosen enemies! Regiments of Renown are unlocked by finding cursed Pieces of Eight throughout the game world, carried by rogue armies that must be defeated.