Can I lower Baron Might with the list?

No, you cannot lower Baron Nashor's Might using the activated ability of The List.

According to the card text for Baron Nashor: "I can't be chosen by enemy spells and abilities."

Because The List requires you to target a unit to give it -2 Might, Baron Nashor's ability prevents him from being a legal target for that effect. Since he cannot be chosen, you cannot lower his Might using that ability.