Sets for Necromancers.

Necromancers benefit the least from it among all factions, as it is their weakest tier 7 creature.

Obtain tier 7 creatures from another castle (preferably an evil one), equip the Lion's Collar before the battle, and you're good to go.
Although, for "evil" factions, the Lion's Collar might not even be necessary, as the morale will be zero anyway.