Text (DI+errata): 2/4. ; When another creature enters the battlefield, sacrifice ~this~. If you do, ~this~ deals 4 damage to that creature. [Oracle 2009/07/08]
If more than one creature comes into play, the ability will trigger more than once, but only the first one to resolve can successfully sacrifice the card, so the damage is only dealt once. [Dissension FAQ 2006/04/13]
