Yeah, that's right and you are about to see it get broken:
Breaking Carnival of Souls
4x Carnival of Souls
4x Soul Warden
4x Bog Rats
4x Unholy Strength
4x Vampiric Tutor
4x Lab Rats
3x Soul Feast
3x Tortured Existence
2x Dark Ritual
4x Thran Quarry
This is simple. Try to get out two Soul Wardens as quickly as possible. You will need one to counteract Carnival of Souls and one to gain an extra life for creatures coming into play.
All of the above creature spells only cost one black to play except for Soul Warden which cost one white. Once you have 2 Soul Wardens in play, cast the Necropotence. If you need to, use the Soul Feast to gain more life. Something like this would be fun:
Turn 1) Play Plains, cast Soul Warden
Turn 2) Play Swamp. Cast second Soul Warden. Cast Dark Ritual and Necropotence. Necro for 10.
Turn 3) Play Swamp. Cast Carnival of Souls. Cast a Lab Rat (At this point you should have 10 cards still in hand.) Let's just assume you have 6 creatures, 3 land, and 1 Unholy Strength. You should be able to cast all 5 creatures (assuming they are not Soul Wardens) and the 2 Unholy Strengths leaving you with 3 lands. You gain 5 more life from the Soul Wardens and you now have 5 1/1 creatures and 1 2/3 creatures on turn 3. NOT BAD AT ALL! Necro for more and do it again! It could use some tweaking but I made this up as I was submitting it.
And who said Carnival of Souls was the worst and most useless card out there? HEH!