The Lord of Night is one of the unique pretenders available to Mictlan. It has several strengths, including a long, flying strategic move, immunity to blinding spells (he doesn't need to see), a strong fear effect, and a paralyzing attack.
But by far the most useful thing about this pretender is that it is an assassin. Not only does he assassinate, but he brings along some friends in the form of beast bats (the description says fiends of darkness, but they lie!). Yes, for early expansion you'd have to look pretty far to find fault in a 90-hit-point flying assassin with death and blood magic for taking out tough independents. The only down-side is that since you will likely be attacking outside your dominion, he probably won't be at full strength.
Giving him some modest boosts to his native paths, you can use this pretender to create a nice Undead Horde.