Sidisi Plan:
Turn 5 Sidisi, sacrifice itself, find Ad Nauseam.
Turn 6 Cast Ad Nauseam, draw your deck, tap your remaining swamp for dark ritual, cast dark sphere, cast sickening dreams with ritual mana, discard 40 swamp. In response to sickening dreams, sac dark sphere. Deal 20 to you and 40 to all your opponents.


Maralen Plan:
Turn 5 Maralen.
Turn 6, Tutor up Ad Nauseam, cast Ad Nauseam, draw your deck, tap your remaining swamp for dark ritual, cast dark sphere, cast sickening dreams with ritual mana, discard 40 swamp. In response to sickening dreams, sac dark sphere. Deal 20 to you and 40 to all your opponents.


Maralen advantages:
Makes your opponents lose 3 life each

Sidisi advantages:
Commander is cheaper
Doesn't give your opponents a tutor while you're waiting