I think you can squeeze one less turn out of this combo by adding in a Lotus Petal, and swapping Lich's Mirror for a less mana-intensive protection. The one that comes to mind is the mana-free (but eats a land drop) Glacial Chasm. So the sequence can look something like this:

1:Play swamp

2:Play swamp

3:Play swamp, Maralen

4:Tutor Ad Nauseum, Play Swamp

5:Tutor Dark Ritual. Cast Dark Ritual (tap 1 swamp). Cast Ad Nauseum (tap 2 swamps, use the mana from the ritual), going through whole deck. Take minor damage from the Sickening Dream. Play Glacial Chasm. Cast Lotus Petal. Sac lotus petal and tap the untapped swamp, use to cast Sickening dream. Discard hand, rain down damage.