As a counterbalance to the leader abilities I proposed in another thread, the evil Minions should be boosted. So:
The Witch King "No living man may hinder me" If eliminated because his army is eliminated, place the Witch King back in the reinforcement pool to show that he may be mustered again as specified on his card. Elimination by a battle card or special ability is still permanent.
Saruman "Bring the Halflings to me" If a Hunt is successful when an Isengard army is located at the Fellowship's last known position, both Hobbit Companions are eliminated in addition to the Hunt damage. For each Hobbit Companion missing from the Fellowship, add one corruption (i.e. if only Merry, add one, if none, add two).
the Mouth of Sauron "the Black Emissary" If the Mouth of Sauron is in an area adjacent to a Free Peoples army with a Companion, the Shadow player may use a Character die and discard a character card to discard an army, muster or event die for the Free Peoples. This may only be done once per turn.
Note: The first is what I've lacked of the Witch King's Nazgûl nature, the second a "light" version of the "Saruman as an independent power" ideas on earlier threads and the third represents the Mouth's evil tidings to Gandalf et al outside the Black Gate...
You can also contemplate adding the following ¨"resurrection" rule for Saruman to these Minion Boosts. This is akin to that for Gandalf the White, but of course far less powerful:
After Saruman is killed, Sharkey may be mustered instead of a Nazgul in a normal SP Mustering action. Sharkey is placed with any Isengard army. He functions with Leadership 1 for movement and battle purposes and has no special anilities. Sharkey is affected by FP Combat Cards as a Nazgul. Once eliminated, he may not be replaced. Use the Saruman miniature to portray Sharkey.