Compared to most turn-1 kill decks, this is cheap and effective, using only one uncommon and one rare:
Swamp
Dark Ritual
Dark Ritual
Wall of Blood, paying 19 life
Sacrifice (You now have 21
)
Repay in Kind (Set all life totals to 1)
You now have 16 mana to deal 1 damage to each opponent. I suggest Syphon Soul.